Hong Life CalculatorsUnderstanding the relative strength calculator — concept and principle
Relative strength expresses how strong you are for your size. The simplest version divides your one-rep max (1RM) by your bodyweight, giving a multiple such as "1.75× bodyweight". The calculator also shows an allometric score, lift ÷ bodyweight^0.67, which is a fairer way to compare light and heavy lifters. People use both to set goals, compare themselves with training partners or follow progress while gaining or losing weight.
How it is calculated
- Bodyweight multiple = 1RM ÷ bodyweight.
- Allometric score = 1RM ÷ bodyweight^0.67.
Use the same unit for both inputs. The multiple has no unit, so it is identical in kg or lb. The allometric score does depend on the unit, so only compare scores calculated in the same unit.
The principle
Muscle force depends mainly on a muscle's cross-sectional area, which grows with the square of body dimensions, while body mass grows with their cube. If two people have the same shape and muscle quality, strength should therefore rise with mass to the power of about 2/3, not in direct proportion. Dividing by bodyweight alone overcorrects and makes heavier lifters look weaker than they are; dividing by bodyweight^0.67 removes most of the size effect. Real data roughly agree, which is why many weightlifting and powerlifting scoring formulas also bend in this way.
Worked example
- Inputs: bodyweight 80, 1RM 140.
- Multiple: 140 ÷ 80 = 1.75×.
- 80^0.67 ≈ 18.84.
- Allometric score: 140 ÷ 18.84 ≈ 7.43.
| Bodyweight | Bodyweight multiple |
|---|---|
| 20 | 7× |
| 40 | 3.5× |
| 60 | 2.33× |
| 80 | 1.75× |
| 100 | 1.4× |
| 120 | 1.17× |
| 160 | 0.88× |
How to read the result
A higher multiple means more strength per kilogram, but the meaning depends on the lift: a 1.75× squat, bench press and overhead press are very different achievements. Typical goals also differ between men and women and by training age. Use the bodyweight multiple to compare yourself with people of similar size, and the allometric score when sizes differ. If you lose fat while keeping your 1RM, both values rise.
Common mistakes
- Comparing multiples across different lifts.
- Mixing kg for one input and lb for the other.
- Comparing allometric scores that were calculated in different units.
- Using an estimated 1RM from very high-rep sets, which can be inaccurate.
Frequently asked questions
Why exactly 0.67?
It is a rounded 2/3, the exponent predicted by geometric scaling. Studies on real lifters give values close to it, though not identical for every lift or group.
Is the bodyweight multiple useless then?
No. It is simple, widely understood and fair enough for people of similar size; it only becomes unfair between very different bodyweights.
Can I use it for pull-ups?
For weighted pull-ups add your bodyweight to the extra load first, since you lift your own body too.
Sources: Jaric S., Muscle strength testing: use of normalisation for body size, Sports Medicine, 2002