Free tool
How strong are you for your bodyweight?
One set and your bodyweight. The Strength Score scales the load by bodyweight, judges the lift against its own standard, and tells you where you land — as a bracket, a band and the next rung.
What is a Strength Score?
A Strength Score is one number for how strong you are across the main lifts, normalised for bodyweight, sex and the lift itself, so that a 60 kg lifter and a 90 kg lifter are measured on one axis and a bench press is not drowned out by a deadlift. Liftor computes it from the estimated one-rep max in each of five movement slots — squat, deadlift, bench, press and row — and shows it on a scale that grows with the load and has no top. In the app it is provisional until five workouts have been logged, because a score from one good set is an anecdote and a score from five sessions is a measurement.
The site’s version runs one set through the same arithmetic. It is the number the app would open with, rounded to a bracket.
How is the Strength Score calculated?
In four steps, each of which the app does the same way. First, each lift’s estimated one-rep max is divided by bodyweight and then corrected for size, because strength does not scale with weight one for one: the term is load ÷ bodyweight × (bodyweight ÷ 80)^0.33, which is load ÷ bodyweight^0.67 anchored at 80 kg. Second, that relative number is divided by the lift’s own “advanced” standard — the bodyweight multiples per lift — so every lift reads on the same scale. Third, the lifts you have are averaged rather than summed, so breadth is rewarded through the fourth step instead: a coverage factor of 0.8 for one lift rising to 1.0 for all five. The one-rep max itself comes from the Epley formula, discounted past twelve reps. The whole formula, term by term, each one worked from the app’s own constants — and the one term that is not published — is on the formula page.
Why is the score scaled by bodyweight?
Because a plain load-to-bodyweight ratio quietly favours lighter people. Muscle strength scales with cross-section, and cross-section grows more slowly than mass, so strength rises with roughly the two-thirds power of bodyweight rather than the first — the allometric relationship Slobodan Jaric set out in Sports Medicine in 2002. Dividing by bodyweight^0.67 instead of bodyweight puts a calisthenics athlete and a heavyweight on the same axis. Sex enters only through the standards table; where it is not given, the app uses the average of the two tables rather than the higher bar, so an unknown never deflates the score.
What do the bands mean?
The bands are names for stretches of the ladder: starting out, novice, intermediate, advanced, elite. They are printed as words because the scale is not a percentage and does not end — the app’s next target is always about ten percent above wherever you are, never less than five and never more than twenty, and the band above is given as a count of those rungs rather than as a number on the scale. Elite is the last band the app names. The rungs keep going.
Why is the number here approximate?
Because it is one set, entered from memory. The app reads a smoothed one-rep max off every set you log, across five movement slots, and applies a recency factor so an old best fades; the site reads one set and treats it as today. The coverage factor lands at 0.84 for a single lift, so the site’s number is an honest floor for the app’s. It also runs without the last term: the scale is set by the Liftor Number, the app’s own calibration per lift and per lifter, and a bracket is as close as a page without it can honestly get. It is shown as a ten-percent bracket for both reasons. The exact number is the app’s to give.
What happens to what you type here?
Nothing, beyond the sum. The arithmetic runs in your browser: what you type is not sent anywhere and not stored, and this page sets no cookie. What the rest of the site keeps is set out in the privacy policy.
Sources
- Jaric S. Muscle strength testing: use of normalisation for body size. Sports Medicine, 2002; 32(10): 615–631
- Epley B. Poundage chart. Boyd Epley Workout. Lincoln, Nebraska: Body Enterprises, 1985
- Liftor’s Strength Score, v2: the allometric term, the standards table, the coverage factor and the five-workout gate (utils/strengthScore.ts in the app’s source); this page runs the site’s mirror of it (lib/strength/estimate.ts)