Estimate your one-rep max (1RM) from a weight and rep count you can currently lift, using the Epley and Brzycki formulas, plus common training percentages of your max.
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Since maxing out on every lift isn't practical or safe for most training, one-rep max (1RM) is commonly estimated from a lighter set taken close to failure. This calculator uses two widely cited formulas: Epley, 1RM = Weight × (1 + Reps ÷ 30), and Brzycki, 1RM = Weight × (36 ÷ (37 − Reps)). The two formulas tend to agree closely at low rep counts and diverge somewhat at higher reps, which is why both are shown alongside their average.
For example, lifting 100 for 5 reps: Epley gives 100 × (1 + 5 ÷ 30) = 100 × 1.167 = 116.7, while Brzycki gives 100 × (36 ÷ (37 − 5)) = 100 × 1.125 = 112.5. The average of the two is 114.6, and 80% of that estimated max is about 91.7.
Many strength programs prescribe working sets as a percentage of your 1RM (for example, '5 sets of 5 at 80% of max'). This calculator shows your estimated max at several common training percentages, so you can quickly translate a percentage-based program into actual weight on the bar.
Estimating from a set that wasn't actually close to failure, the formulas assume the entered reps represent close to maximum effort at that weight, a set with several reps left in reserve produces an inflated 1RM estimate.
Using a very high rep count (above about 10-12) for the estimate, both formulas become progressively less reliable outside their originally studied rep ranges.
Re-testing 1RM (real or estimated) too frequently, strength changes gradually, testing every session adds fatigue without meaningfully new information.
It's a reasonably close estimate for most people when based on a set of 10 reps or fewer taken close to failure, but individual factors like muscle fiber type and training experience mean actual 1RM can differ from the estimate by a meaningful margin.
Epley and Brzycki were derived from different data sets and use different mathematical relationships between reps and percentage of max, so they naturally diverge somewhat, especially at higher rep counts. Neither is universally 'more correct', which is why this calculator shows both.
That's a personal training decision best made with appropriate experience, warm-up and, ideally, a spotter. Many lifters find estimated 1RM from submaximal sets is perfectly sufficient for programming purposes without needing to test a true max.
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