Use this free online one rep max calculator to estimate the heaviest weight you could lift for a single repetition, using the Epley formula. Enter the weight you lifted and how many reps you performed to see your estimated one rep max plus a reference table of equivalent weights at other rep counts.
The calculator uses the Epley formula, one of the most widely used rep-max equations in strength training: One Rep Max = Weight × (1 + Reps ÷ 30).
In plain terms, every extra rep you complete adds about 3.3% of the bar weight to the estimate. A set of 10 reps suggests the weight was roughly 75% of your maximum, and a set of 5 reps suggests about 86%. If you enter a single rep, that weight is already your one rep max, so it is shown as it is rather than scaled up.
The formula has no units of its own. Enter the weight in kilograms and the result is in kilograms; enter pounds and you get pounds. Count only the bar and plates (or the machine stack) you actually moved, and use the same unit for every lift you track.
Suppose you bench press 60 kg for 8 clean reps. The estimate is 60 × (1 + 8 ÷ 30) = 60 × 1.2667 = 76.00 kg. The table under the result then works backwards from 76 kg: about 69.09 kg for 3 reps, 65.14 kg for 5 reps, 60.00 kg for 8 reps (your original set) and 57.00 kg for 10 reps.
Other formulas give slightly different answers. The Brzycki formula, Weight × 36 ÷ (37 − Reps), puts the same set at about 74.5 kg. A spread of a kilogram or two between methods is normal, which is why any rep-based figure should be treated as an estimate and not as a guaranteed lift.
This is the relationship the calculator uses. The last column shows the working weight for someone whose one rep max is 100 kg, so you can scale it to your own number.
| Reps | Approx. % of 1RM | Weight if 1RM is 100 kg |
|---|---|---|
| 1 | 100% | 100 kg |
| 2 | 93.8% | 93.8 kg |
| 3 | 90.9% | 90.9 kg |
| 5 | 85.7% | 85.7 kg |
| 6 | 83.3% | 83.3 kg |
| 8 | 78.9% | 78.9 kg |
| 10 | 75.0% | 75.0 kg |
| 12 | 71.4% | 71.4 kg |
| 15 | 66.7% | 66.7 kg |
Many strength programmes prescribe loads as a percentage of your one rep max, for example 5 sets of 5 at 75%. With an estimated maximum of 76 kg, 75% works out to 57 kg; round to the nearest weight you can actually load on the bar.
Estimating your maximum from a moderate set is also safer than testing a true single, which puts heavy load on joints and needs a spotter or safety bars. Beginners, and anyone with high blood pressure, a heart condition or a recent injury, should get advice from a doctor or qualified coach before attempting maximal lifts. Re-estimate every few weeks, because the number should rise as you get stronger.