Definition of

Yocto-

A prefix meaning one-septillionth (1/1,000,000,000,000,000,000,000,000 or 10-24)

The same as multiplying by 10-24 (which is 0.000 000 000 000 000 000 000 001)

Prefix is y

Example: 12 yg = 12 yoctograms = 0.000 000 000 000 000 000 000 012 g

The rest mass of a proton is 1.6726 yg

Yocto-