One-Rep Max (1RM) Calculator
Estimate your one-rep max from a set taken to near failure using the Epley and Brzycki formulas, with a full percentage-of-1RM training table.
How it works
Epley: 1RM = w × (1 + reps ÷ 30) · Brzycki: 1RM = w × 36 ÷ (37 − reps)
Your one-rep max is the most weight you can lift once, but testing it directly is risky, so it is usually estimated from a lighter set taken close to failure. The Epley and Brzycki formulas both convert weight and reps to a 1RM and agree closely in the 1–10 rep range, drifting apart as reps climb. Because accuracy falls with higher reps, use a set of about 3–8 reps for the best estimate, and treat the number as a training guide rather than a guaranteed lift.
Worked example
Lifting 100 kg for 5 reps: Epley gives 100 × (1 + 5 ÷ 30) = 116.7 kg, and Brzycki gives 100 × 36 ÷ (37 − 5) = 112.5 kg. Programming at 80% of 116.7 kg means working sets near 93 kg.
Sources: One-repetition maximum
Frequently asked questions
How accurate is an estimated 1RM?
Estimates are most reliable from sets of 3–8 reps taken near failure, usually within a few percent of a true max. Above 10 reps, fatigue and technique vary too much for a precise number.
Which formula should I use?
Epley and Brzycki are the two most common and agree closely for low reps. Epley tends to read slightly higher at more reps; try both and use the average if you like.
How do I use percentages of 1RM?
Programs prescribe loads as a percentage of 1RM — for example 5×5 at 80%. The table above converts your estimated max into working weights and the reps each load roughly allows.
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Educational estimate using standard formulas and population averages — not medical advice. Talk to a qualified clinician before making decisions about diet, training, or pregnancy.