How the 1RM Calculator Works
Enter a weight you lifted and the number of reps you completed. The calculator estimates your one-rep max using three proven formulas, then averages them to produce a projected max. Below that, a full percentage chart shows what each rep range corresponds to at your estimated 1RM, with RPE (Rate of Perceived Exertion) mapped alongside.
The Three Formulas
| Formula | Equation | Best For |
|---|---|---|
| Epley | weight × (1 + reps/30) | General use. Slightly favors higher rep ranges. |
| Brzycki | weight × 36/(37 - reps) | Lower rep ranges (2-6). Most conservative for high reps. |
| Lombardi | weight × reps0.1 | Moderate estimate across all rep ranges. |
How Accurate Is This?
All 1RM formulas are most accurate between 2 and 10 reps. In that range, the estimates typically land within 5% of your actual max. Beyond 10 reps, accuracy drops significantly — endurance and fatigue start skewing the math. For competition planning, nothing replaces testing actual heavy singles in training.
Tips for a Better Estimate
Use a weight you've lifted recently with clean form. Don't use a set where you ground out ugly reps or had a spotter help. A solid set of 3-5 at a challenging weight will give you the most reliable number. If you have multiple recent sets, run them all through the calculator and look for consistency.