There is the quantity given by the equation:

gamma = 1 / sqrt(1 - ((V^2) / (c^2)))

where,
sqrt() means take the square root of the quantity in the brackets
V = velocity in meters per second
c = speed of light = 300,000,000 meters per second

V^2 means velocty squared
c^2 means the speed of light squared

If you plug in a bunch of numbers for velocity, create a table of velocty versus gamma factor, for speeds ranging from 0 thru 299,999,999 m/s, then you get a good reference table for looking up stuff.

All you have to remember is that time slows down, length contracts, mass increases --- ALL BY THE SAME AMOUNT.