# Siff's Bodymass Adjustment Formula

## ...for the Squat, Bench Press, Deadlift and Powerlifting Total

*Scroll down for introduction and
usage instructions.*

### About

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.

The formulas are presented in Dr. Siff's legendary book Supertraining (see chapter 3.3.5), but an excerpt can also be found online. For reference, here are the formulas:

```
```**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.