Sperm Whales Statistics. Maximum length: 18m (60ft) males / m (41ft) females, average around 16m. Adult weight: 63 tonnes males max. / 27 tonnes. Jump to External appearance - The name sperm whale is a truncation of spermaceti whale. Spermaceti, originally mistakenly identified as the whales' semen, is the semi-liquid, waxy substance found within the whale's head (see below).Species: P. macrocephalus.