One Rep Max Calculator
Estimate your one-rep max from a weight and 1–20 repetitions using the Epley and Brzycki formulas, with an average estimate and a 50–95% reference table in kg and lb.
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About the One Rep Max Calculator
One Rep Max Calculator estimates the most weight you could lift for a single repetition, based on a weight you lifted for several repetitions. Enter the weight, choose kilograms or pounds, and enter how many repetitions you completed (1 to 20). The tool shows the Epley and Brzycki estimates side by side, a clearly labelled average of the two, and every result in both kg and lb.
A reference table lists 50% to 95% of the estimate you choose. These are mathematical estimates only: they become less reliable as repetitions increase, and the tool does not recommend weights, programmes, technique or maximum testing. Never attempt a lift based on these numbers alone, and consult a qualified professional if you have an injury, health condition or exercise restrictions.
How to use
- Optionally type the exercise name so it appears in your summary.
- Enter the weight lifted and choose kg or lb.
- Enter the number of repetitions you completed (1–20).
- Click Calculate to see the Epley, Brzycki and average estimates.
- Choose which estimate the percentage table uses, then copy or download the summary.
Key features
- Epley: weight × (1 + reps ÷ 30).
- Brzycki: weight × 36 ÷ (37 − reps).
- Average of both estimates, clearly labelled.
- Results in kilograms and pounds.
- Reference table from 50% to 95% of the selected estimate.
- Reliability notes for 1 repetition and for more than 10 repetitions.
Best practices
- Use a set you completed with good form, not a failed attempt.
- Sets of about 2–10 repetitions give the most consistent estimates.
- Use the estimate as a rough guide, not a target to test.
- Track estimates over time with the same exercise and method.
- Seek professional guidance before heavy lifting if you have any health concerns.
Benefits
- Compare two widely used formulas at once.
- Avoids the need to test a true maximum.
- Works in kg or lb with instant conversion.
- Private and free — runs in your browser.
Frequently asked questions
How do the Epley and Brzycki formulas work?
Epley estimates 1RM as weight × (1 + reps ÷ 30). Brzycki estimates it as weight × 36 ÷ (37 − reps). Both use the weight and the number of repetitions you completed.
Why are the two estimates different?
They are different mathematical models. They agree closely at low repetitions and drift apart as repetitions increase, which is why the tool shows both and an average.
Why is the limit 20 repetitions?
Estimates become unreliable at high repetitions, so the calculator only accepts 1 to 20. Even within that range, results above about 10 repetitions should be treated as rough.
What happens with 1 repetition?
If you completed 1 repetition, that weight is your actual single-lift result. Brzycki returns it exactly, while Epley adds about 3%.
Is the percentage table a training plan?
No. It is simple arithmetic showing percentages of the estimate. The tool does not recommend what weight to lift, how many sets to do or whether to test a maximum.
Is it safe to lift my estimated 1RM?
The tool cannot tell you what is safe. Estimates can be wrong, and maximal lifts carry risk. If you have an injury, health condition or exercise restrictions, consult a qualified healthcare or fitness professional.