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One-rep max calculator
Turn any set into an estimate of the heaviest single you could lift today. Add the set's RPE for a fairer number, then use the result to plan the loads for your next session.
Calculate it
Estimated one-rep max
123.3kg
Read from the RPE chart: 5 reps at RPE 8 is 81.1% of a max. A close estimate.
What that max predicts
| 1 rep at your limit | 123.3 kg |
|---|---|
| 3 reps at your limit | 113.7 kg |
| 5 reps at your limit | 106.4 kg |
| 8 reps at your limit | 96.9 kg |
| 10 reps at your limit | 91.1 kg |
| 12 reps at your limit | 83.8 kg |
| 15 reps at your limit | 78.3 kg |
Load for a planned set
Load the bar to about 100 kg for 5 reps at RPE 8.
Other formulas, same set
| Epley | 116.7 kg |
|---|---|
| Brzycki | 112.5 kg |
How the estimate works
Every set sits on one curve: the heavier the weight, the fewer reps you can do with it. The calculator reads that curve from the RPE percentage chart popularised by Reactive Training Systems and studied by Zourdos and colleagues (2016). It counts the reps you did plus the reps you had left in reserve (10 minus RPE), and looks up what percentage of a one-rep max that combination represents.
A set of 100 kg for 5 at RPE 8 is 5 reps with 2 left, which the chart puts at 81.1% of a max, so the estimate is 123.3 kg. Log the same set with no RPE and the calculator has to assume you went to your limit, so it gives 115.9 kg. The difference is the two reps you did not show.
Past the end of the published chart, the curve continues with the same shape as the Epley formula, so very high-rep sets still get an estimate, flagged as rough. For the same 100 kg × 5, Epley alone gives 116.7 kg and Brzycki gives 112.5 kg: classic formulas assume every set was taken to failure.
RPE chart: percentage of your one-rep max
Read across from the reps you did to the RPE you rated the set. Multiply your one-rep max by the percentage to get a working weight, or divide a working weight by it to estimate your max.
| Reps | RPE 10 | RPE 9 | RPE 8 | RPE 7 | RPE 6 |
|---|---|---|---|---|---|
| 1 | 100.0% | 95.5% | 92.2% | 89.2% | 86.3% |
| 2 | 95.5% | 92.2% | 89.2% | 86.3% | 83.7% |
| 3 | 92.2% | 89.2% | 86.3% | 83.7% | 81.1% |
| 4 | 89.2% | 86.3% | 83.7% | 81.1% | 78.6% |
| 5 | 86.3% | 83.7% | 81.1% | 78.6% | 76.2% |
| 6 | 83.7% | 81.1% | 78.6% | 76.2% | 73.9% |
| 7 | 81.1% | 78.6% | 76.2% | 73.9% | 70.7% |
| 8 | 78.6% | 76.2% | 73.9% | 70.7% | 68.0% |
| 9 | 76.2% | 73.9% | 70.7% | 68.0% | 66.4% |
| 10 | 73.9% | 70.7% | 68.0% | 66.4% | 64.9% |
| 11 | 70.7% | 68.0% | 66.4% | 64.9% | 63.5% |
| 12 | 68.0% | 66.4% | 64.9% | 63.5% | 62.1% |
When to trust it, and when not to
- Low reps estimate best. Sets of 1 to 6 reps land close to a tested max. Above 10 reps, two lifters with the same max can differ by several reps at the same weight.
- RPE has to be honest. Calling a grinder RPE 8 inflates the estimate. If you are not sure, leave RPE out and accept the conservative number.
- Fatigue counts. Your fourth set of the day estimates lower than your first. Compare estimates from the same position in a session.
- It is a trend line, not a test. Watch the estimate rise over weeks. Do not choose a max attempt from a single set.
Planning a session from your max? The plate calculator tells you what to load on the bar.
Questions
How accurate is an estimated one-rep max?
Close for sets of about 1 to 6 reps with an honest RPE, and increasingly rough above 10 reps, where people differ most in how many reps they can do at a given percentage. Use it to track a trend over weeks, not to pick a weight for a max attempt.
Which formula does this calculator use?
The RPE percentage chart (Reactive Training Systems, studied by Zourdos and colleagues in 2016): a set is converted using its reps plus its reps in reserve. Without an RPE the set is treated as a true max, RPE 10. Epley and Brzycki are shown alongside for comparison.
Do I need to record RPE?
No, but it makes the estimate fairer. Five reps that left three in the tank say more about your strength than five reps to failure, and only RPE can tell the two apart.