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One Rep Max Calculator
Estimate your one-rep max from a weight and rep count using the Epley or Brzycki formula, plus a full training-percentage breakdown. Runs entirely in your browser.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
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Example shown — enter your own lift. Best accuracy is at 10 reps or fewer.
Training percentages
| % of 1RM | Weight |
|---|
How it works
- Enter the weight you lifted and how many reps you completed.
- Pick a formula — Epley, Brzycki, or the average of both.
- See your estimated 1-rep max and the weight for common training percentages.
The formulas
Epley: 1RM = Weight × (1 + Reps ÷ 30)
Brzycki: 1RM = Weight × 36 ÷ (37 − Reps)
Example: 100 kg for 5 reps gives an Epley estimate of 100 × (1 + 5/30) ≈ 116.7 kg.
FAQ
What's the difference between the Epley and Brzycki formulas?
Both estimate a 1-rep max from a lighter set taken to (or near) failure, but with slightly different curves — Epley tends to estimate a bit higher at higher rep counts, Brzycki a bit lower. Neither is universally "correct"; picking one and using it consistently to track progress matters more than which one.
Why does the tool warn about reps over 10?
Both formulas get less reliable as rep count climbs, since they're extrapolating further from a true 1-rep effort. A near-max single or a 3-5 rep set gives a much more trustworthy estimate than a 15-20 rep set.
What are the training percentages for?
Many strength programs prescribe work sets as a percentage of your 1-rep max (e.g. "3 sets of 5 at 80%"). Once you have an estimated max, the table converts that straight into the actual weight to load for each percentage.
Should I actually attempt a true 1-rep max to test this?
Not necessarily — that carries more injury risk, especially without a spotter. An estimated max from a comfortably-heavy set is the safer, and for most training purposes, sufficiently accurate alternative.
How we compare
| Feature | Online Tool Store | Strength Level | Gym whiteboard math |
|---|---|---|---|
| Multiple formulas plus a training-percentage table | ✓ | Single formula, strength charts | Manual, error-prone |
| No sign-up | ✓ | ✓ | ✓ |
| No ads | ✓ | Ad-supported | ✓ |
Getting straight to "what weight is 80% of my max" beats doing that math on a gym floor between sets.