How to use the 1RM Calculator
- Enter the weight you lifted for a hard set with clean technique.
- Enter the number of repetitions completed — accuracy drops badly above about ten.
- Read the estimated one-rep max and the percentage table.
- Re-test with the same rep range so week-to-week comparisons stay valid.
How the calculation works
Repetition formulas assume a roughly linear relationship between load and reps over low rep ranges. The Epley formula, used here, adds about 3.3% of the lifted weight per repetition performed. Brzycki and Lombardi produce slightly different estimates from the same input, which is why an estimate should always be described together with the formula and rep count that produced it.
Accuracy is best from two to six repetitions. Beyond ten, muscular endurance and mental tolerance start to dominate, and the estimate drifts high — a set of twenty says more about conditioning than about maximal strength. Estimates also differ by lift: they tend to hold well for squat and bench press and to overstate deadlift and overhead press for many lifters.
1RM = w × (1 + reps / 30) (Epley)Source: Epley B., 'Poundage Chart', Boyd Epley Workout, 1985; comparisons per Brzycki and Lombardi rep-max equations.
Worked example
A lifter completes 5 clean reps of a 122.5 kg back squat, with maybe one rep left in reserve.
- reps / 30 = 5 / 30 = 0.1667.
- 1 + 0.1667 = 1.1667.
- 122.5 × 1.1667 ≈ 142.9.
Estimated 1RM ≈ 143 kg. Training percentages: 85% ≈ 121 kg, 75% ≈ 107 kg, 65% ≈ 93 kg.
Frequently asked questions
How many reps give the most reliable estimate?+
Between two and six. That range is close enough to maximal effort that the linear assumption holds, while still being safe to perform without a spotter's full attention on a limit attempt.
Why is my estimated max higher than what I can actually lift?+
Estimates assume the set was genuinely near failure with the same technique you would use at a max, and they overstate lifts where technique degrades under maximal load — deadlift and overhead press especially.
How often should I re-estimate?+
Every four to six weeks, or at the end of a training block. Use the same lift, rep range and equipment so the comparison reflects strength change rather than a change in test conditions.
Can I use this for machine exercises?+
Only within the same machine. Leverage, cable ratios and weight stack increments differ between manufacturers, so a machine estimate does not transfer to free weights or to another gym's equipment.
Last reviewed August 31, 2026. We review this page whenever the underlying formula, tax year, published rate or standard changes.