Relative Strength Ratio Calculator
Compare lifters of different sizes with a raw bodyweight ratio and an allometric (2/3-power) strength index.
How it works
Relative strength = lift ÷ bodyweight · allometric index = lift ÷ bodyweight^(2/3)
A plain lift-to-bodyweight ratio favours lighter lifters, because strength does not rise in direct proportion to bodyweight — it scales closer to bodyweight to the two-thirds power, following how muscle cross-section grows relative to mass. The allometric index divides the lift by bodyweight^(2/3) to compare lifters of very different sizes more fairly, the same idea behind official powerlifting scoring formulas without tying you to one federation's coefficients.
Worked example
A 405 lb lift at 180 lb bodyweight is 405 ÷ 180 = 2.25× bodyweight. The allometric index is 405 ÷ 180^0.667 = 405 ÷ 31.9 ≈ 12.7, a figure you can compare against a heavier lifter whose raw ratio would otherwise look worse.
Frequently asked questions
How is this different from a Wilks score?
Wilks and similar scores use a fitted polynomial coefficient specific to powerlifting totals. This uses the simpler, general allometric 2/3-power law, so it works for any single lift or total without federation-specific tables.
Why the two-thirds power?
Muscle force tracks cross-sectional area, which scales with the square of a length, while mass scales with the cube. The ratio of the two is the 2/3 power, so strength is expected to grow with bodyweight^(2/3).
Can I compare men and women with this?
The index removes the bodyweight advantage but not physiological differences, so it is best for comparing lifters of the same sex. Cross-sex comparisons still need sex-specific coefficients.
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Educational estimate for training planning, not medical or coaching advice. Warm up, use good form, and progress gradually — stop if you feel pain.