The time to boil crab depends on the type and size of the crab, but generally it ranges from about 7 to 15 minutes. For example:

• Blue crabs are typically boiled for about 8 to 10 minutes after the water returns to a boil once the crabs are added. Some sources recommend 5 to 15 minutes depending on crab size.

• Dungeness crabs take about 12 to 15 minutes to boil whole. If cleaned and halved, they take 10 to 12 minutes.

• Generally, boil the crabs until they turn bright red-orange in color, which signifies they are cooked through.

• After boiling, crabs are often soaked in the boiling liquid or an ice bath for several minutes to stop cooking and help absorb flavors.

So, the recommended boiling time for crab is typically between 8 to 15 minutes depending on crab type and size, followed by a cool-down or soaking period. If boiling crab legs, which are usually pre-cooked, the goal is to reheat them, typically for about 30-45 minutes with seasoning in water.

Hence, for most whole crabs, boiling for about 10 to 15 minutes after the water returns to a boil should be sufficient.