Scroll down for introduction and usage instructions.
This calculator computes bodyweight-adjusted relative strength scores for the three powerlifts (squat, bench press and deadlift) and totals (combined score for the three powerlifts) using formulas developed by the late South African sport scientist Dr. Mel C Siff. The Siff score represents a percentage of a World Record performance for the lifter's weight based on actual powerlifting data up to the year 1987. For an introduction on what relative strength is and more on the origins of these formulas, see the about section of the Powerlifting Relative Strength Calculator. Also note that if you are interested in gender and age adjusted totals, you should use that calculator. The Wilks formula it contains has also been validated for use in the bench press, so that could be an option if you want to gender or age adjust scores for only the bench.
Total lifted T = a - b*B ^(-c)
where B = bodymass and a, b and c are numerical constants.
For powerlifting data up to 1987, the values of the constants are:
Powerlifting Total: a = 1270.4, b = 172970, c = 1.3925
Powerlifting Squat: a = 638.01, b = 9517.7, c = 0.7911
Powerlifting Bench Press: a = 408.15, b = 11047, c = 0.9371
Powerlifting Deadlift: a = 433.14, b = 493825, c = 1.9712
How to use the calculator is hopefully self-explanatory, but do not hesitate to contact me (see e-mail at the bottom of the page) with feedback or questions.