1-Rep Max Calculator
Estimate your one-rep max from a weight and rep count you can already do.
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How to estimate your one-rep max
- Enter a weight you lifted and choose kg or lb.
- Enter how many clean reps you managed with it.
- Read your estimated 1RM from two formulas, and a table of training percentages.
The formulas
Epley: 1RM = weight × (1 + reps ÷ 30). Brzycki: 1RM = weight × 36 ÷ (37 − reps) — this one is undefined at 37 reps and unreliable well before that, so treat any high-rep estimate from either formula as a rough ballpark rather than a number to load on the bar.
Nothing entered here is sent to a server — the entire calculation runs as JavaScript in your browser tab.
Questions about one-rep max
What is a one-rep max?
The heaviest weight you could lift for a single repetition with good form. Programmes often prescribe training weights as a percentage of it.
How do I estimate it without testing a max lift?
Lift a weight you can manage for 3 to 10 good reps and enter it here. 100 kg for 5 reps gives an estimate of about 117 kg with the Epley formula.
How accurate are the estimates?
Most accurate from sets of about 10 reps or fewer. From high-rep sets, treat the result as a rough guide, not a weight to load on the bar.
Why are there two numbers?
Epley and Brzycki are the two most widely used formulas. They agree closely at low reps and drift apart as reps go up; the training table uses their average.