One Rep Max Calculator
Estimate your 1RM from a submaximal set and get a full percentage training table.
Please note: For general information only. This is not medical advice — speak to a doctor or registered dietitian before changing your diet, training or medication.
What the One Rep Max Calculator does
One rep max is the heaviest weight you can lift once with good form. Testing it directly is risky and fatiguing, so these formulas estimate it from a submaximal set — the standard approach in strength programming.
Formula
Epley: 1RM = w × (1 + reps ÷ 30)Brzycki: 1RM = w × 36 ÷ (37 − reps)Lombardi: 1RM = w × reps^0.10
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Weight lifted | number | Yes | Accepts 1 or more. |
| Repetitions completed | number | Yes | Accepts 1 or more, up to 20. |
| Formula | one of 4 options | Yes | — |
| Unit | one of 2 options | Yes | — |
How to use it
- Choose Formula and Unit.
- Enter Weight lifted and Repetitions completed.
- Select Calculate.
Worked example
You bench press 100 kg for 5 reps.
- Weight
- 100
- Reps
- 5
- Formula
- Epley
100 × (1 + 5/30) = 116.7 kg estimated 1RM.
Reading the result
- The estimate gets less reliable the further the submaximal set is from failure or the higher the rep count — a 3-rep estimate is generally more trustworthy than a 12-rep one, since the underlying formulas were built from lower-rep data and extrapolate further at higher reps.
Common mistakes
- Treating the estimated 1RM as a number to actually attempt without a spotter or safety bar. It is a training-table input, not a verified maximum.
Frequently asked questions
How accurate are these estimates?
Within about 5% when the set is in the 3–8 rep range and taken close to failure. Beyond 10 reps the error grows quickly.
Which formula is best?
Epley tends to read higher at high rep counts, Brzycki lower. For most lifters the difference is small — pick one and use it consistently to track progress.
Method and sources
Method. Three published submaximal prediction equations — Epley, Brzycki and Lombardi — from the weight lifted and the repetitions completed, with the option to average them.
Assumptions
- The set was taken close to failure with consistent form; a set stopped several repetitions short predicts a maximum that is too low.
- The equations were derived from trained adult populations performing standard barbell lifts.
Limitations
- Accuracy falls away as repetitions rise. Above roughly ten, the equations diverge from each other and from reality, because endurance rather than strength starts to set the limit.
- The three formulas disagree by design — comparing a figure from one against a target set with another is not meaningful, which is why all three are shown.
- A predicted maximum is not a lift you have performed. Treat it as a training input, not a number to attempt without preparation and a spotter.
Sources
- Poundage chart, in “Boyd Epley Workout”, p. 86 — Body Enterprises, Lincoln, Nebraska (Boyd Epley), 1985. The Epley equation.
- Strength Testing—Predicting a One-Rep Max from Reps-to-Fatigue — Journal of Physical Education, Recreation & Dance 64(1):88–90 (Brzycki), 1993. The Brzycki equation.