One Rep Max Calculator
Estimate your one-rep max from the weight and reps of a lifting set.
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How it works
Your one-rep max (1RM) is the most weight you can lift for a single rep. Rather than testing it directly, you can estimate it from a lighter set taken near failure. This tool uses two well-known formulas — Epley (weight × (1 + reps/30)) and Brzycki (weight × 36 / (37 − reps)) — and averages them. It also prints a percentage table (50% to 95% of 1RM) so you can pick training loads. Estimates are most accurate under about 10 reps. All math runs in your browser.
Epley 1RM = weight × (1 + reps / 30)
Brzycki 1RM = weight × 36 / (37 − reps)
Common use cases
- Estimating your max squat or bench without a risky max attempt.
- Setting working weights as a percentage of your 1RM.
- Tracking strength progress over training blocks.
Frequently asked questions
How accurate is the estimate?
These formulas are reliable for low rep counts (roughly 2 to 10 reps). Accuracy drops with high-rep sets, where fatigue and endurance affect the result more than raw strength. Averaging Epley and Brzycki smooths out each formula's bias.
Why is there a percentage table?
Most strength programs prescribe loads as a percentage of 1RM — for example 5 sets of 5 at 80%. The table converts your estimated max into those working weights instantly.
Should I actually attempt my estimated 1RM?
Only with proper warm-up, technique, and ideally a spotter. The estimate is for programming; a true max attempt carries injury risk and is not necessary to train effectively.