One-Rep Max Calculator
Estimate your one-rep max and training percentages for any lift from a weight and rep count using this free 1RM calculator.
Enter Values
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the weight lifted and reps.
- Press Calculate.
How it works
Estimates the most you could lift once from a lighter set, using the Epley formula: weight × (1 + reps ÷ 30).
Worked example
100 kg for 5 reps. ≈ 117 kg.
Common mistakes
- Estimating from high-rep sets — accuracy drops fast above about 10 reps, so use a heavy set of 3–6 for the best estimate.
- Treating the estimate as a guaranteed lift — always test a true 1RM with a spotter and a proper warm-up.
Frequently asked questions
Which 1RM formula does this use?
It applies the Epley and Brzycki estimates; both are reliable in the 1–10 rep range and agree closely for low reps.
How often should I retest my one-rep max?
Every 4–8 weeks is plenty — frequent maximal testing adds fatigue and injury risk with little training benefit.
How accurate is an estimated 1RM?
It's a close estimate from a lighter set and becomes less reliable above about 10 reps. Use it as a guide and always lift with safe form and a spotter.
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Cite this tool
Zerdly. (2026). One-Rep Max Calculator. Retrieved from https://www.zerdly.com/tools/one-rep-max-calculator/
Tip: Enter any known values to calculate the remaining results.
Designed to run locally in your browser. Tool inputs are not intentionally stored by Zerdly unless stated otherwise.