One-Rep Max Calculator
Estimate your 1-rep max from a weight and reps performed.
Input sheet
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Your one-rep max is the most you can lift for a single rep — the benchmark that drives smart strength programming. This tool estimates it from a set you've actually done, so you can program working weights without a risky maximal attempt.
How it works
Epley formula: 1RM = weight × (1 + reps ÷ 30). Most accurate for sets under about 10 reps.
The headline uses the Epley formula, which estimates 1RM as the weight times one plus reps divided by thirty. The tool also shows the Brzycki estimate as a cross-check, since the two formulas diverge slightly at higher rep counts.
Accuracy is best for sets under about ten reps. Beyond that, fatigue and endurance muddy the relationship between reps and true strength, so the estimate drifts. Use a heavier, lower-rep set for the most reliable number.
Epley: 1RM = weight × (1 + reps ÷ 30). Brzycki: 1RM = weight × 36 ÷ (37 − reps).
Worked examples
Lifting 185 lb for 5 clean reps. → Estimated 1RM about 216 lb; an 85% working set ≈ 183 lb.
185 × (1 + 5 ÷ 30) ≈ 215.8; 215.8 × 0.85 ≈ 183 lb.
Lifting 225 lb for 3 reps. → Estimated 1RM about 248 lb.
225 × (1 + 3 ÷ 30) = 225 × 1.1 = 247.5 lb.
Tips & gotchas
- Always warm up thoroughly and use a spotter or safety pins before testing anything near your true max.
- Use the 1RM estimate to set percentages — most strength work lives in the 70-90% range, where this tool's working-set figure helps.
- Re-estimate from a fresh set every few weeks; chasing the formula daily just adds fatigue.
- If your test set was above ten reps, trust the number less — redo it with a heavier weight and fewer reps.
FAQ
Why do the Epley and Brzycki estimates differ?
They're separate formulas fit to different data. They agree closely at low reps and drift apart as reps climb. Seeing both gives you a sensible range rather than a single false-precision number.
Do I have to actually max out to know my 1RM?
No — that's the point of this tool. A submaximal set of a few reps estimates your max safely, avoiding the injury risk of a true single-rep attempt.
Why is accuracy worse at high reps?
High-rep sets test muscular endurance as much as pure strength, so the rep-to-max relationship breaks down. Sets of 1-6 reps give the most reliable estimate.
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