My eyesight is -10.25 in both eyes. how bad is this? is this legally blind

Probably not: A level of -10.25 is highly myopic but if correctable to 20/20 with proper eyeglasses or contacts, then you definitely are not legally blind. Legal blindness refers to the best corrected vision/ not to the uncorrected vision. Your level of myopia is high but not extreme. Contact lens manufacturers pre-make soft lenses in the most common powers from 0.00 to -12.00. So they think -10 is common.