[header] How to identify whales [title] Estimate the whale's size. [step] You may only see part of the animal, so figuring out its length can be difficult. Try to compare it to the length of a nearby object, such as a boat. 
Estimate the whale's general size range, such as 10 to 20 ft (3.0 to 6.1 m). [substeps] For example, animals under 10 ft (3.0 m) are probably dolphins or porpoises.