Strength
One-rep max calculator: the Epley formula, worked once
You do not have to test a max to know it. One honest set is enough, up to a point, and the point is twelve reps.
Calculate your one-rep max
Estimated one-rep max
—kg
Type a weight and the three formulas answer. Epley is the app’s; the other two are there to show how little they disagree.
| Reps | % of 1RM | Load (kg) |
|---|---|---|
| 1 | 100% | — |
| 2 | 94% | — |
| 3 | 91% | — |
| 4 | 88% | — |
| 5 | 86% | — |
| 6 | 83% | — |
| 7 | 81% | — |
| 8 | 79% | — |
| 9 | 77% | — |
| 10 | 75% | — |
| 11 | 73% | — |
| 12 | 71% | — |
Nothing typed here leaves the page. The app runs this on every set you log and smooths it across sessions, which is the number the Strength Score reads.
How do you estimate a one-rep max from a set?
Multiply the weight by one plus the reps divided by thirty. That is the Epley formula, published by Boyd Epley at the University of Nebraska in 1985 and still the most used: 1RM ≈ weight × (1 + reps ÷ 30). A set of 100 kg for five reps estimates a max of 100 × (1 + 5 ÷ 30) = 116.7 kg. A single rep is taken as read; the formula is only for sets of two or more.
It is an estimate, and it is a good one in the range it was built for. Different lifters and different lifts fall on slightly different curves, which is why a predicted max and a tested max can disagree by a few kilograms in either direction. Other formulas exist — Brzycki and Lombardi are the common ones — and below ten reps they agree with Epley within a few percent, which is inside the noise of a single set anyway.
Where does the formula break?
Past about ten to twelve reps. The relationship between reps and load is close to linear at low rep counts and flattens as the reps climb, so a set of twenty extrapolates to a max that nobody could lift. Liftor discounts any estimate taken from more than twelve reps — the app’s own cap — and the site’s free tools take twelve reps at most, with a note that past that it is cardio.
The other limit is honesty. Epley assumes the set went to, or very near, failure. A set of five with three reps in reserve was really a set of eight; the formula cannot see the reserve, so Liftor reads it from the RIR you log instead.
What does Liftor do with the number?
It runs the formula on every logged set, smooths the estimate across recent sessions so one bad night does not move your max, and keeps one per movement slot — squat, deadlift, bench, press, row. Those five estimates are the inputs to the Strength Score, which scales each by bodyweight and judges it against that lift’s own standard. On the site you can run one set through the same arithmetic; the app runs all of them, every time you train.
How much do the one-rep max formulas disagree?
By a few kilograms below ten reps, and by more past it. The three you will meet are Epley, weight × (1 + reps ÷ 30); Brzycki, published by Matt Brzycki in 1993, weight × 36 ÷ (37 − reps); and Lombardi, weight × reps^0.1. For 100 kg lifted five times they say 116.7, 112.5 and 117.5 kg. For 100 kg lifted ten times, 133.3, 133.3 and 125.9. At twelve reps they have drifted to 140, 144 and 128, which is the polite way the arithmetic tells you it has left the range it was built for.
| 100 kg for | Epley | Brzycki | Lombardi |
|---|---|---|---|
| 3 reps | 110.0 | 105.9 | 111.6 |
| 5 reps | 116.7 | 112.5 | 117.5 |
| 8 reps | 126.7 | 124.1 | 123.1 |
| 10 reps | 133.3 | 133.3 | 125.9 |
| 12 reps | 140.0 | 144.0 | 128.2 |
Liftor uses Epley because it is the simplest of the three and the one most other tools use, so the number in the app matches the number you would work out on a napkin. The spread between the formulas is smaller than the spread between two of your own sets a week apart, which is why the app smooths across sessions rather than trusting any single estimate.
How often should you test a real one-rep max?
Rarely, and never because an app asked. A true single costs a session, needs a spotter or safeties, and tells you something the estimate already knew to within a few percent. Powerlifters test on the platform, at the end of a peak, because the number on the day is the point of the sport; for everyone else the estimated max is the more useful figure, because it updates every session instead of every few months and it is measured on the reps you actually train.
Nothing in Liftor prescribes a max attempt. The Strength Score reads a smoothed estimate off every set you log, discounts anything taken from more than twelve reps, and lets an old best fade with a recency factor, so a personal record on a set of five moves the number the same afternoon. If you want to test one anyway, do it at the end of a block, after a deload, on a morning the readiness score likes.
Sources
- Epley B. Poundage chart. Boyd Epley Workout. Lincoln, Nebraska: Body Enterprises, 1985
- Brzycki M. Strength testing — predicting a one-rep max from reps-to-fatigue. Journal of Physical Education, Recreation & Dance, 1993; 64(1): 88–90
- Liftor’s estimator: Epley on every set, a single rep taken as read, estimates past twelve reps discounted (utils/strengthScore.ts, REP_CAP_FOR_E1RM)