What is a 1RM (one rep max)?
Your 1RM is the maximum weight you can lift for one repetition with proper form on a given exercise. It is the standard reference point for strength training programming - most plans prescribe working weights as a percentage of 1RM. The catch is that testing your actual 1RM is risky: it requires near-maximal effort under heavy loads, and a missed attempt at high weight is where most training injuries happen. An estimated 1RM, calculated from a submaximal set, is almost always the better choice.
The 4 formulas explained
All four formulas use the same inputs (weight and reps) but apply slightly different math. Each was developed from different research datasets, so each has small biases. Averaging them produces a more reliable estimate than any single formula.
- Epley (1985): weight × (1 + reps/30). The most widely used formula in strength training apps. Tends to slightly overestimate at higher rep ranges (8+).
- Brzycki (1993): weight × 36 / (37 - reps). More conservative than Epley at typical training rep ranges (1-10), but becomes more aggressive at very high rep counts (12+). Common in powerlifting circles.
- Lander (1985): (100 × weight) / (101.3 - 2.67123 × reps). Very close to Epley in middle rep ranges. Specifically calibrated for the bench press.
- Lombardi (1989): weight × reps^0.10. Uses a power function rather than linear math. Stays close to other formulas at low reps, becomes notably more conservative at higher rep ranges (8+).
Why an estimated 1RM beats a tested 1RM
Three reasons. First, every working set you do is already a data point - you do not need a separate testing session to know your strength. Second, repeated maximal attempts are the highest-injury-risk training you can do, especially without a competent spotter. Third, your tested 1RM on any given day is biased by sleep, stress, food, and warm-up quality. An estimate from a moderate working set, averaged across 4 formulas, smooths out daily noise and gives a more honest picture of your real strength.
How to use these numbers in your training
For percentage-based programs like 5/3/1, multiply your estimated 1RM by 0.85 or 0.90 to set your Training Max - the value all your working percentages reference. For double progression, use the rep target table to pick a starting weight at the bottom of your chosen rep range. For deload weeks, drop your working weight to 50-60% of your 1RM and keep the same reps. The same number drives all three decisions. See our 5/3/1 program guide, progressive overload guide, and deload week guide for the full programming context.
Frequently asked questions
How accurate is an estimated 1RM?
Within 5-10% of your actual 1RM for most lifters at most weights, when calculated from a set in the 2-10 rep range. Accuracy drops at higher rep counts (12+) because muscular endurance starts to matter more than pure strength. Use submaximal sets for the most reliable estimates.
Should I test my real 1RM?
Rarely. Competitive powerlifters need tested maxes for meets. Most other lifters get more value from a continuous trend of estimated 1RMs across months than from one tested number. The risk-reward of true 1RM testing rarely justifies the injury exposure.
Which formula is the most accurate?
There is no single winner. Each formula has small biases at different rep ranges. The average of all four is more reliable than any single one. That is the headline number this calculator displays.
Can I use this for any exercise?
Yes for compound barbell movements (squat, bench press, deadlift, overhead press, row). Less reliable for isolation exercises and dumbbell movements where larger weight increments (often 2 kg jumps) and higher stabilization demands skew the math. Most useful as a barbell strength estimator.
Why do percentages above 95% drop off?
Above 95% of true 1RM, every additional kilogram requires disproportionately more effort. The percentage tables in this calculator stop at 95% because that is the practical training ceiling - above that, you are testing maxes, not training.
