Crab legs come in a set of ten. A true crab has five pairs of legs: one pair of claws (chelipeds) at the front and four pairs of walking legs behind them. So the full count is 10 legs, or 8 walking legs plus 2 claws. That is why crabs belong to the decapods, a name that means “ten feet”.
Many people guess eight, because the claws do not look like legs. However, biologists count them, since the claws grow from the same body segments as the walking legs.
How Crab Legs Are Counted
For example, scientists call the ten legs pereiopods. In addition, a crab has three pairs of small maxillipeds near its mouth. Those are mouthparts that hold and tear food, so they are not legs and do not change the total.
| Pair | Common name | Main job |
|---|---|---|
| 1st | Claws (chelipeds) | Feeding, defense, signaling to mates |
| 2nd to 4th | Walking legs | Walking, climbing, gripping |
| 5th | Walking legs, or paddles in swimming crabs | Walking or swimming |
| Total | 5 pairs | 10 legs |
What Different Crab Legs Do
First, the claws do most of the handling. A crab uses them to pick up food, crack shells, fight rivals and wave at mates. In many species, males also carry noticeably bigger claws than females.
Next, the walking legs carry the body. Because each leg bends mainly sideways, most crabs walk side to side faster than forward.
Finally, swimming crabs change the last pair. For example, the blue crab has three pairs of walking legs and flat, paddle-shaped rear legs for swimming, according to the Chesapeake Bay Program field guide. Even so, those paddles are still part of the ten.
Crabs That Seem to Have Fewer Crab Legs
A few animals called crabs look like they have only eight legs. However, they are not true crabs. Instead, they belong to a related group that evolved a crab-like shape.
- King crabs. At first glance, you see six walking legs and two claws. The fifth pair is tiny and sits inside the gill chamber, where it cleans the gills.
- Hermit crabs. Meanwhile, their small rear legs stay tucked inside the borrowed shell, so only the front legs show.
- Porcelain crabs. Similarly, they hold a small last pair of legs folded against the body.
As a result, the count you see can be eight while the real count is still ten.
How Long Can Crab Legs Get?
Also, crab legs vary hugely in size. Leg span is measured from the tip of one leg or claw to the tip of the opposite one, with the legs stretched out. By contrast, body size is usually given as carapace width, the widest point of the shell.
| Crab | Record size (US) | Metric |
|---|---|---|
| Japanese spider crab | Leg span up to 12.5 ft, up to 42 lb | 3.81 m, 19.05 kg |
| Red king crab | Leg span up to 5 ft, up to 24 lb | 1.52 m, 10.89 kg |
| Blue crab | Shell up to 9 in across | 22.86 cm |
The figures come from National Geographic for the spider crab and from NOAA Fisheries for the red king crab. To picture smaller sizes, see how long 6 inches is.
Convert a Crab Leg Span to Metric
First, enter a leg span or shell width below. The converter then shows it in meters, centimeters, inches and feet, using the exact definition 1 ft = 0.3048 m.
Can Crabs Regrow Lost Crab Legs?
Yes. For instance, a crab can drop a leg on purpose to escape a predator, and it seals the wound quickly. Then a small new leg forms under the shell and grows larger with each molt. Therefore, you may see a crab with one leg clearly shorter than the rest; it is often a regrowing limb.
Crab Legs FAQs
How many crab legs does one crab have?
A true crab has 10 legs: 2 claws and 8 walking legs, arranged in five pairs.
Do crabs have 8 or 10 legs?
They have 10. After all, the two claws count as legs, so 8 walking legs plus 2 claws make 10.
Are claws counted as crab legs?
Yes. Biologists count the claws as the first pair of legs, because they grow from the same body segments.
Why does a king crab look like it has 8 legs?
Its fifth pair of legs is tiny and hidden inside the gill chamber, so you mostly see six walking legs and two claws.
Do crabs have arms?
No. Instead, the claws act like arms, but anatomically they are the first pair of legs.
What are the swimming legs on a blue crab?
In other words, they are the last pair of the ten legs, flattened into paddles for swimming.
Can a crab live with missing legs?
Often, yes. In fact, a crab can drop a leg and regrow it over several molts.
Which crab has the longest legs?
The Japanese spider crab, with a leg span of up to about 12.5 ft (3.81 m).
Why do crabs walk sideways?
Their leg joints bend mainly sideways, so moving sideways is faster and easier for most crabs.
What does decapod mean?
Decapod means “ten feet”. In addition, it is the group that includes crabs, lobsters and shrimp.
The Bottom Line
In short, a crab has 10 legs: 2 claws and 8 walking legs. Hidden or paddle-shaped last pairs do not change that count. For more on the units used in the size table, see metric vs imperial.