Although the different species of sea turtles have a lot in common, their sizes vary drastically. The smallest species are the olive and Kemp’s ridley turtles which usually grow to between 58 and 78 centimetres. They are the only two species that don’t reach a full metre in length. The hawksbill and flatback sea turtles have an average length of 90 to 100 centimetres, and the loggerhead and green sea turtles have an average length of 90 to 120 centimetres. The leatherback sea turtle is by far the largest, ranging between 1.6 and 2.4 metres in length.