One of the biggest contributors to the size of your frog is the size of his tank. The larger the tank, the larger the frog will grow. However, as was said before they often have growth spurts. They will remail a certain size for a period of time (sometimes longer than we think they should) and then one day you’ll go to feed your frog and realize it has doubled in size…since yesterday. That may be somewhat of an exageration, but they do tend to grow overnight without you realizing it.

Try putting your frog in a tank that seems entirely too large for him and wait. One day you’ll get a surprise. Also keep in mind that depending on whether you have a male or female will determine size as well. The females will be considerably larger.

Enjoy your frog and if it’s big enough, try rubbing it’s belly. They tend to like that. (in the water, don’t try to take it out)
References :

African Clawed Frog

Xenopus Laevis
Description:
A plump, medium-sized (5 inches) aquatic frog with smooth, slippery skin, large, webbed rear feet and clawed front legs. Color ranges from greyish to brownish, marbled with darker shades (the underside is generally creamy white), though albino varieties are also rapidly becoming popular for pet keeping.
Often these frogs are confused for their smaller cousin, the African Dwarf Frog.
How to tell the Clawed Frog from the Dwarf Frog.

Habitat:
Warm, quiet waters. A warm fishtank with water at least 30cm (12 in) deep around 24?C (75?F) is recommended, with gravel substrate and a filter. (Preferably with hiding place. Frogs tend to get a bit freakish if they can’t sometimes hide.)
Also, these guys need a really good cover so they don’t go exploring outside their tank!
Now I’m going to tell you a very sad story;
Several years ago, my sister got 2 Albino African Clawed Frogs. The pet store sold them as African Dwarf frogs (they look pretty similar when young…though I’ve never seen albino dwarf frogs).
Well, she thought they were really cool and named them Humpty and Dumpty). They were housed in a hexagon plastic tank full of water (the gallon and a half size) along with a huge goldfish. This setup would probably have been just fine for dwarf frogs, but the clawed frog is more likely to be "hoppity" and managed to jump through a small opening in the top (which I think was supposed to be for air filters and heaters etc.) and it hopped all the way out of her bedroom, all the way down the stairs, all the way to the living room, where it stuck itself to a window and dried up.
It was the saddest, most pathetic thing you ever saw …so close to freedom and yet so far!
The next frogs my sister got were truly dwarf frogs and no such problems occured.
The moral of this story is, make sure that all openings are well sealed, either with a net or something so that they can’t get out! I get mail all the time from people with stories like this!
I also got a story with a not so sad ending:
Hi, My name is Chris. I have an African frog that I used to keep in a very cool aquarium that I have. It is a 60 Hex that is 4 feet tall and 12 inches wide(side to side). This take also has a stand and cap, each one being adding 1 foot the the height of the aquarium. I once discovered, to my dismay, that he had escaped one day. I searched all over my room and around my apartment. I couldn’t find him. The next day, my room mate got home(who actually owns the frog, but keeps him in my tank since he has proven himself inept at being an aquarist) and I told him. We both looked around and he found the frog by the door to the patio. When I first saw the frog I was instantly reminded of the desciated, flattened frogs seen on the roadside after losing a fight with a car. We both were sure he was dead. I went ahead a put him in some water just to be sure, but when he just sank and didn’t move, I took him out. I was morbidly curious about the frog so I took a close look at him. I was amazed at how much dust he had collected and how rubbery his skin had become. Then I was even more amazed to see his nostrils move. Here was this desicated little frog(about a year old) with rubberized skin, dust, hair, sunken in eyes and no discernible life signs, except his nostrils were moving! I quickly put him back in the bowl of water but drained it so that his nostrils were above water. Then I took a wet paper towel and very gently cleaned all the dust and stuff off of him. Within a few hours, he began moving(a little) and his eyes took on their normal shape again. In the next few days, some of his fingers, skin and webbing came off and we again were worried whether or not he could recover enough to eat and keep healing(he had been fed on guppies). Fortunately, I fed him some blood worms and I put 1 guppy into the bowl with him as he recooperated. After a few days, he ate the guppy and I knew he was going to be alright. About a month later he has regrown all his fingers, skin, and webbing. He has also not been given the opportunity to escape again. Hard to believe, but this little frog survived a six foot jump(narrowly missing the light) to the the floor and a 2 day safari into the dusty depths. I’m gonna try to get my roommate to rename him to Evil Kanevil.

Read more information on tank set-up in the Housing Your Pet Frog section.
(see the Frog Doctor for details on illness prevention.)
Diet:
Brine shrimp, and various commercial fish foods. These guys are scavengers, meaning they’ll pretty much eat anything they can swallow. They find their prey by smell and touch.
One visitor recommended Tetra’s ReptoMin. "It contains all the vitamins and such, though I have found they prefer to have each stick broken into at least three pieces. I think this is a vital piece of info for your sheet. People may be taken aback at having to feed just shrimp or feeder fish as the cost can really get up there. ReptoMin can be gotten cheaply (especially if by mail order) and last a good long while. I use feeder fish only as a treat with ReptoMin as the only other food sorce. I have had my frogs a number of years (not one sickness to date) and had one successfull breeding, so it must be good food."
Another writes that "specially-formulated food for ACFs is available at xenopus express for only $3.00 a pound (much more cost-effective than ‘Reptomin’ — $30+ per pound)."
Habits:
Calm. These guys are incredibly hardy and live a long time. Dont believe me on this one? Here’s the most impressive testimonial I’ve heard yet, sent in by a visitor in June, 1999! (Note: the frog described is probably a Clawed Frog, because Grow-A-Frog kits never sold Dwarf Frogs in their kits.)

Many years ago I saw one of the Grow-a-Frog kits in an upscale toystore for the 1st time. Couldn’t resist. So bought 2. Sent one to my nephew and kept one. He wasn’t as lucky as I was. His tadpole came, began to metamorphose, but died before completing the process. Mine finished the process and still lives. It never occurred to me to note the year, for who would have thought he’d live so long! It was either 1980 or 1981, but no later. He’s just fine and still sings when I clean his bowl. I’ve changed containers over the years to different shapes and slightly different sizes to offer some variety in his life. As far as I’ve been able to tell, he’s never been sick a day in his life. He may be a she. Many dogs, cats, gerbils, rats, tropical fish, one snapping turtle, and one cockatiel have become members of our family. All lived full lives and went to pet heaven & received burial in our flower beds. Neighbors always fed our menagerie when we went on vacations, but as the years ticked away, they worried that our frog might die on "their watch." They were as relieved as we, each time we returned to find everything OK including our beloved frog.
I’m a science teacher, but think that has little to do with our frog’s longevity. My daughters are both grown and on their own. I guess I should start thinking about who I should entrust him with in my will. I’ve always assumed he was an African Dwarf. We didn’t name him for many years because we never expected him to live much longer. After a while, when visitors always exclaimed, "You mean that frog is still ALIVE?", we started calling him "Alive."

I sold my large house after 27 years of loving it & moved to a condo in a downtown historical district. Fortunately, the re-location didn’t bother him a bit. That was 2 years ago, & he’s just fine.

These frogs also are pretty fun to watch. They do a loop-de-loop dance in the water from the tank floor to the top of the water when they mate, usually preceeded by a lot of "clasping", where the male grabs onto the female as she swims around. (It looks a lot like "hugging" to me) Tadpoles hatch within two days.

How to Tell Males from Females:
Females are often larger and fatter than males, and they have a little extension between their legs (see photo). The frogs mature after 10 months to a year, and the males begin vocalizing at this age in the evening hours. males also develop dark mating pads on the undersides of their hands and arms.
(Click picture to see it bigger)
Photo copyrights:
"CBC"
Reptiles & Amphibians: Care & Culture Carolina Biological Supply Company ? 1993,
ISBN 0-89278-040-1
"NAS"
Amphibians: Guidelines for breeding, care and management of laboratory animals
National Academy of Sciences ? 1974, ISBN 0-309-02212-X

Miscellaneous Facts:
Xenopus means literally: "strange foot"…derived from the sharp claws on the toes of their large, strong, webbed hind feet. These guys are primarily from Southern Africa, though they were also introduced to California waters (where they rapidly became a dangerous pest – eating just about everything they could get their claws on.) I read recently somewhere, however, that its now believed that these (californian frogs) are dying out.
http://allaboutfrogs.org/info/species/clawed.html

INFO & CARE SHEET
for the
AFRICAN CLAWED FROG

Introduction

Although the African Clawed Frog, Xenopus laevis, is
commonly seen in captivity, little authoritative information on its
husbandry and breeding is available to the lay public. Given the fact
that this frog has been known to science since the 19th century, such
a conspicuous lack of information is truly amazing. It is also
unfortunate, as the African Clawed Frog makes an ideal pet for
seasoned herpetoculturists and rank novices alike, if its unique needs
are appropriately met. Questions regarding proper food, housing,
lighting, temperature, etc. are constantly encountered not only on
USENET’s rec.pets.herp discussion group but also in other
herpetocultural fora as well. Hopefully, this sheet will be able to
clarify the African Clawed Frog’s basic requirements so that owners
will finally be able to feel confident their charges are receiving the
best possible care.

Background

The African Clawed Frog exemplifies the notion that nature is
loathe to mess with a successful adaptation. Well-preserved fossils
of Xenopi have been found from the Cretaceous, and the laevis
is nowhere endangered even today. On the contrary, human commerce
has served to establish viable colonies of these anurans in a number
of areas well outside their home range, such as southern California
and Arizona. For the ostensible purpose of stopping their
uncontrolled spread, legislation prohibiting their possession is in
effect in these and numerous other regions. Thus, local ordinances
should be consulted before a decision is made to accommodate
Xenopi, and they should never be released into the wild anywhere
or under any circumstances.
Xenopi are grouped in Family Pipidae, all of whose members
are wholly aquatic and tongueless. In addition, all Pipids embody a
number of other exceptional characteristics: a wedge-shaped body
which is dorsoventrally flattened, small, upward-gazing eyes, no
visible eardrums, unique vocalizing apparatus requiring no inflatable
sacs, no teeth, very slippery integument, etc. Xenopus laevis is
perhaps the best known of the 14 species in Genus Xenopus. All
are native only to sub-Saharan Africa, where they are commonly
known as Platannas. The term "Xenopus" is Latin for "peculiar foot,"
an apt description of the enormous webbed, five-toed, three-clawed
rear feet typical of the group. "Laevis" means "smooth." Other
Pipids include the so-called Surinam Toad (Genus Pipa) of Central
and South America, perhaps one of the world’s strangest looking
anurans, as well as the diminutive West African Hymenochirus and
Pseudohymenochirus.
To obtain a feeling for Xenopus husbandry, one must
understand how they live in the wild. The Clawed Frog is
preeminently a creature of stagnant pools and backwaters arising on
a substrate of deep mud. Its highly-developed lungs enable it to
obtain practically all necessary oxygen at the surface; indeed,
without constant access to air it will quickly succumb. Thus,
Xenopi patrol a markedly turbid fluid environment often choked
with rotting organic matter. Their incredibly sensitive fingertips,
four on each hand, and sophisticated lateral line systems allow them
to locate living prey easily, even when it is concealed in mud and
detritus. Given these inhospitable conditions, however, they have
also evolved the ability to locate by smell and efficiently consume
nonliving food items–a rare adaptation in anurans and one which
often gives the Xenopus a significant advantage when
inadvertently transplanted to other parts of the globe.
Because the Clawed Frog’s niche precludes holding physical
territory as more terrestrial counterparts do, this anuran customarily
utilizes survival strategies which minimize competition with adult
conspecifics. For example, females tend to quietly reconnoiter areas
above the water’s surface for prospective meals, while males often
prefer actively searching for food across the bottom.
When the Clawed Frog’s shallow haunts dry out, as they
frequently do during long hot summers, it burrows up to one foot
into the mud to aestivate, carefully arranging the tunnel so an air
hole remains open. Xenopi can spend up to ten months in this
inactive state. Captive Clawed Frogs can live 15 years, but typical
life spans for wild and feral Xenopi, including those which
aestivate, have not been ascertained.
While Clawed Frogs are not known to be toxic to any animal,
they possess chemical defenses which give protection against both
predators and diseases. The mildly fishy smell they exude repels
many vertebrate predators, especially those found outside of the
Xenopus’ native range. In addition, they generate organic
compounds called magainins which have powerful antibiotic,
antifungal, antiparasitic, and antiviral actions. Ongoing research on
magainins and other substances produced by Clawed Frogs has
already given rise to some useful pharmaceuticals, with many more
in the offing.
The Xenopus laevis was the first vertebrate to be
successfully cloned and has traveled aboard the Space Shuttle on
several occasions.

General Husbandry of Juvenile & Adult Clawed Frogs

The African Clawed Frog’s ideal captive environment is one
which mimics as closely as possible the natural conditions under
which it is normally found. The following should be employed as
basic guidelines:

Housing

These are strictly aquatic anurans. At least 1 gallon of water
per animal, with the depth no more than 12 inches and no less than
six. Do not use distilled water. Bottles of tap water should stand
open for at least 1 day before being poured into the tank to outgas
chlorine and related chemicals. Alternatively, 2 tiny (1 mm cube)
crystals of sodium thiosulfate can be added to each gallon bottle at
least 1 day prior to use.
African Clawed frogs are specifically adapted for stagnant
water conditions. Although aesthetically pleasing to the keeper
mechanical and/or electrical filtration invariably produces adverse
long-term effects on the frogs. Constant water movement no matter
how slight is sensed through the highly developed lateral-line
system and results in severe stress. The effect is insidious and can
be compared to what would happen to a human if (s)he were
compelled to live where sandblasters and jackhammers were in use
24 hours a day.
99 % of the water should be changed by bailing, siphon, and/or
spigots every 3-4 days, or whenever it becomes extremely cloudy.
When in doubt about changing the water, try to err on the side of
cleanliness, though extreme fastidiousness is unnecessary. At every
water change use a towel to remove any algae and accumulated
exudate which form on the tank walls, but do not use any type of
algae-inhibiting or water-purifying chemicals other than the
minuscule amount of sodium thiosulfate mentioned above.
Metal ions are toxic to Xenopi, lowering their resistance to
infection. Make absolutely certain there is no metal of any kind in or
on the tank or upon which water can splash and drip back into the
tank, e.g. from a screen or light fixture. Never clean the tank with
soaps or caustics or allow such compounds to come in contact with
the water. Do not use pest-strips or insecticides in the vicinity of the
tank.
The Clawed Frog is quite comfortable in ascetic surroundings,
provided they are suitably spacious. Do not use a substrate of small
stones, as these can be accidentally ingested. Avoid living plants, as
the frogs uproot them quickly. A few sterilized medium-to-large
rocks are sufficient to break up the physical monotony of a plain
tank.
Adult Xenopi may be gently handled, although they’re
notoriously slippery. They must never be netted, however, because
their thin fingers may be inadvertently entangled and amputated by
even the finest mesh. Since they desiccate easily they must never be
kept in a dry situation for more than a few minutes.

Lighting & Temperature

Avoid extremes. In particular, do not expose the tank to any
direct sunlight, very bright artificial light, or temperatures above 90
degrees or below 40 degrees F. The frogs are most comfortable with
indirect lighting during regular daylight hours and a temperature
range of from 60 to 80 degrees F., i.e. customary indoor temperature.
As a rule of thumb, if you’re comfortable in the environment where
the tank is located, Xenopi will be too. Clawed frogs have no
special ultraviolet lighting requirements.

Food

Xenopi should be fed once a day with as much food as they
will consume in 15 minutes. Avoid overfeeding; it only clouds the
water. Content African Frogs will often take food from their keeper’s
fingers. They’ll nibble the keeper too, but their toothless mouths
can’t do any damage. In the wild, Clawed Frogs are happy to dine on
living, dead, and dying arthropods, bits of organic garbage, and loose
material from putrefying corpses of miscellaneous vertebrates. For
captive specimens, Reptomin ™ sticks are excellent basic fare as
are many other heavily proteinaceous foods compounded primarily
for aquatic turtles.
There are several biological supply houses (e.g. Three Rivers
Amphibian, Carolina Biological, etc.) which offer balanced food
formulated specifically for this anuran. Pieces of lean raw beef,
insects and larvae, cat and dog food, shrimp, worms, etc. may be
offered. Supplementation with calcium or vitamins is unnecessary if
professionally balanced formula foods are used as a dietary staple.

Tadpoles
The broad, shallow aquatic expanses which are home to the
Xenopus assure minimal contact between healthy frog larvae and
adults. But in captive situations the two must be kept completely
separate; even freshly metamorphosed Xenopi will quickly make a
meal of sibling tads if given the chance.
Clawed frog tadpoles have catfish-like barbels and swim in a
head-down position. They have somewhat different requirements
than their metamorphosed conspecifics. In particular, they are
exclusively filter-feeders with no rasping mouthparts. Thus, unless
food circulates freely in their water as micron-sized particles it
cannot be utilized. To assure the proper degree of fluid circulation
around each tad, their tails vibrate continuously in a manner
reminiscent of a gray flame burning beneath the water.
No matter how large or small the tank there should be no less
than 1 pint of water per tadpole. Powdered egg is an ideal food, but
goldfish flakes ground extremely fine with mortar and pestle may be
used as an alternative. Each tad should receive only enough powder
per day to lightly cover a 14-point capital letter O. Overfeeding tads
poses a real danger to the animals, as their gills cannot process
needed oxygen when the water is clogged with particulate food.
98 % of tadpole water must be changed once a day, even if it
appears to be perfectly clear. Clawed Frog tads are extremely
delicate and should not be touched or netted. Their beating hearts
and coiled silvery intestines are clearly visible through transparent
skin. Xenopi often produce a high percentage of genetically
defective offspring.

Mating

Xenopi are sexually mature at 10 months to 1 year. At that
time sexing is easy. Males vocalize frequently during evening hours,
have a smooth rump, are 1/2 the size of females, relatively skinny,
and develop dark mating pads on the undersides of their hands and
forearms. Females are chubby, almost entirely silent, and possess a
cloacal extension; they range between 3 and 6 inches snout-to-vent.
Mating via inguinal amplexus can take place at any time but is
more common during the spring; up to four matings per year have
been reported for compatible couples. Many interesting and
provocative techniques have been attempted to encourage mating,
but the results remain controversial. One factor is clear, however:
the frogs must be given substantially more room than usual. For 2
males and 2 females, 5 to 50 gallons of water at a depth of 8 to 9
inches is adequate. Water should be kept as clean as possible, and its
temperature should be around 70 degrees F. Mating often takes
place late at night when the frogs detect no other activity, so it is
challenging to observe. Sticky eggs are cast loose singly, with
hundreds extruded during a 3 to 4 hour period. Within obviously
narrow limits, the speed of metamorphosis is directly proportional to
the water temperature. The average interval from egg to froglet is
about 6 to 8 weeks.
Metamorphosis is a critical event, since the entire circulatory,
digestive, and nervous systems are reorganized in a short space of
time. The keeper must be particularly concerned about the radical
change in eating habits: while Clawed Frog tadpoles must filter-feed,
the short gut of newly transformed juveniles (and subsequent
adults) can only accommodate visible solid food.
To insure only appropriate fare is offered, the following should
be carefully observed. Massive morphological changes will be noted
soon after the front limbs appear, and the tail’s energetic vibrations
will slow and finally stop. During this period, feeding with powdered
food should continue as usual. However, when the tail clearly begins
to degenerate the frog is deriving nourishment from it alone, and
feeding is not necessary. In this very brief interim, lasting on the
average of 4-5 days, when the animal is balanced on a
developmental edge between tadpole and frog, no external
nourishment can be absorbed. Soon, the tail shrinks to nothing but a
small stump. At this point adult food should be offered. The newly
metamorphosed frog’s first regular meal should be particularly
appetizing: a few small slivers of lean, raw beef are good. The period
between formation of the front legs and first acceptance of solid food
is around 10 days.
Xenopus froglets are fragile creatures small enough to fit on
an average-sized postage stamp; tads are considerably longer. Their
rear legs are so transparent the femurs can be seen clearly. Over the
next few months the frog’s natural coloration will appear, and their
legs will become opaque. Simple vocalizations from males may be
heard as soon as months after metamorphosis.

Final Notes

While the Clawed Frog may be commonly encountered in both
laboratories and the pet trade, it is not a boring animal. A strikingly
"social" and intelligent anuran, its lifestyle still holds many mysteries
for those who have not lost the capacity to wonder at nature. For
example, no one yet knows how many calls Xenopi utilize or the
characteristics and purposes of such vocalizations.
A partial bibliography is appended to this sheet. While much
information on the Xenopus is squirreled away in obscure
academic literature, those with the time, energy, and fortitude to
peruse it will encounter many fascinating intellectual treats.
A long-time confirmed fan of the Xenopus laevis, the author
has tried his best to do justice to basic Clawed Frog husbandry in a
condensed format. To accomplish this he has drawn liberally from
personal, testimonial, popular, and scientific sources. Still, if errors
large or small have crept in, they are his responsibility alone and
much regretted.

Happy herping!
References :