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One Rep Max (1RM) Calculator

All 7 formulas. Full percentage chart for programming. Mobile friendly.

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Exercise

Weight lifted (kg)

Reps completed

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How to Use 1RM in Training Programming

The one rep max (1RM) is the maximum weight a person can lift for one complete repetition of a given exercise. It is the foundation of percentage-based strength programming — all training weights are expressed as a percentage of 1RM. You do not need to test 1RM directly; this calculator estimates it from any submaximal set.

Most accurate range: 1RM estimates are most accurate when calculated from sets of 3-6 reps. Sets above 10 reps introduce greater error due to fatigue effects. For best accuracy, use a weight your client can lift for 4-6 clean reps with 1-2 reps in reserve.

Why 7 formulas? No single formula is universally most accurate. Epley and Brzycki are the most commonly used. For clients with slow-twitch muscle dominance (endurance athletes), Mayhew tends to be more accurate. Showing the average of all 7 gives the most reliable estimate.

FAQs

Is the 1RM calculator accurate?

Estimates are typically within 5-10% of actual 1RM for sets of 3-6 reps. Accuracy decreases with higher rep sets. Individual response to fatigue, training age, and muscle fiber type all affect accuracy. Use it as a programming guide, not a competition standard.

How often should 1RM be recalculated?

For intermediate and advanced clients, recalculate every 4-8 weeks as strength improves. For beginners, recalculate every 2-3 weeks as they improve rapidly. After deload weeks or illness, use a conservative estimate (90-95% of previous 1RM) when returning to training.

What percentage of 1RM is best for hypertrophy?

Research shows muscle growth occurs across a wide range (30-85% of 1RM) when sets are taken close to failure. The traditional hypertrophy range of 65-80% 1RM (8-15 reps) is effective because it allows enough volume while maintaining technique. Higher percentages build more strength simultaneously.

Can I use 1RM calculations for women clients?

Yes. The formulas are the same regardless of gender. Strength differences between males and females are reflected in the absolute weight used, not in the mathematical relationship between submaximal performance and 1RM.