Difference in Size
The majority of squid are no more than 60 cm long, although the giant squid may reach 13 m in length. There have even been claims reported of specimens of up to 20 metres (66 ft).
Octopuses grow in size from upto 1cm to about 5m. They have a short life span and may not live upto more than 4 to 5 years but can grow quite heavy in weight.
Locomotion
Octopuses and squids move by "jet propulsion", sucking water into a muscular sac in the mantle cavity surrounding their bodies and quickly expelling it out a narrow siphon. Octopuses and squids can swim in any direction and can alter their course quickly. Squids use fins located on their heads to propel themselves when swimming at low speeds. These fins steer and stabilize the squids when moving slowly, and wrap around the body when they move quickly, by way of jet propulsion. Most octopuses do not have fins as adults. Some deepwater octopuses are exceptions. The eyes of a Squid, found on either side of the head, each contain a hard lens. The lens is focused by moving, much like the lens of a camera or telescope, rather than changing shape like a human eye.