Enter the weight you lifted and how many reps you did to estimate the heaviest weight you could lift once. It averages five common formulas and gives a percentage table.
Results are estimates for planning. Check the figures before you make a financial or health decision.
How the One-rep max calculator works
A one-rep max (1RM) is the most you could lift for a single repetition. Rather than test it directly, the calculator estimates it from a lighter set using five well-known formulas, then averages them. With weight w and reps r:
- Epley: w × (1 + r ÷ 30)
- Brzycki: w × 36 ÷ (37 − r)
- Lander: 100 × w ÷ (101.3 − 2.67123 × r)
- Lombardi: w × r^0.10
- O’Conner: w × (1 + 0.025 × r)
If you enter 1 rep, the weight itself is the 1RM. Reps must be whole numbers from 1 to 12, because the estimates become unreliable for high-rep sets. A percentage table from 95% down to 50% of the 1RM gives working weights, rounded to the nearest 0.5 kg or 1 lb, with the rough number of reps usually possible at each level.
Worked example
Using the default values in the calculator above:
| Input | Value |
|---|---|
| Weight unit | Kilograms |
| Weight lifted | 80 |
| Repetitions completed | 6 reps |
Estimated one-rep max (average of five formulas): 94.1 kg
| Epley | 96 kg |
|---|---|
| Brzycki | 92.9 kg |
| Lander | 93.8 kg |
| Lombardi | 95.7 kg |
| O’Conner | 92 kg |
| 95% of 1RM, about 2 reps | 89.5 kg |
Tips and common mistakes
The estimate is best from a hard set taken close to failure with good technique, so use one that really challenged you. The formulas agree closely at low reps and drift apart as reps rise. Rep numbers beside each percentage are averages: some people manage more, particularly on big leg lifts. Do not attempt a true one-rep max unless you have experience, warm up well and have a spotter or safety bars. This is general information, not medical advice.
Frequently asked questions
Which one-rep max formula is the most accurate?
None is best for everyone. Epley and Brzycki are the most used, and averaging several, as this tool does, smooths out the differences.
How many reps should I use?
Sets of about 3 to 8 reps near failure usually give the most reliable estimate. Sets above 10 reps are less accurate.
Is it safe to test my true 1RM?
It carries more risk than lighter sets. If you want to try, warm up thoroughly, use a spotter or safety bars, and consider using the estimate instead.
Guides that help
- One-rep max guide: how to estimate your 1RM and use it in training
- Heart rate zones explained: how to find your maximum and train by zone