One-Rep Max Calculator
Estimate your one-rep max from the weight and reps of a working set, using the Epley and Brzycki formulas.
The heaviest weight you could likely lift once, from 100 kg × 5 reps.
| % of 1RM | Reps | Weight (kg) |
|---|---|---|
| 100% | 1 | 115 |
| 95% | 2 | 109.5 |
| 90% | 4 | 103.5 |
| 85% | 6 | 98 |
| 80% | 8 | 92 |
| 75% | 10 | 86.5 |
| 70% | 12 | 80.5 |
Lift 100 kg for 5 reps? Epley estimates your one-rep max at 100 × (1 + 5 ÷ 30) = 116.7 kg, while Brzycki gives 100 × 36 ÷ (37 − 5) = 112.5 kg. Averaging the two formulas puts your estimated 1RM near 115 kg — the most you could lift once.
What a one-rep max is
Your one-rep max (1RM) is the heaviest weight you can lift for a single, full repetition of an exercise. It is the standard benchmark for strength and the reference point for programming: most training percentages, from a 5×5 to a peaking block, are written as a fraction of your 1RM. Testing a true 1RM is taxing and risky, so lifters usually estimate it from a set they have already done.
This calculator takes a submaximal set — a weight you lifted for a known number of reps — and projects the load you could handle for one rep. It runs two well-established formulas, Epley and Brzycki, then averages them, because no single equation is right for everyone. The two agree closely at low reps and drift apart as the rep count climbs, which is exactly why seeing both is useful.
w = weight lifted, reps = repetitions completed to failure. When reps = 1 the 1RM is simply w. This tool reports both estimates and their average.
Worked example: 100 kg for 5 reps
Run the same set through both formulas, then take the average:
- 1 Record a working set. Note the weight and how many clean reps you completed — e.g. 100 kg for 5 reps. Keep the rep count in the 1–10 range for the best accuracy.
- 2 Apply the Epley formula. 1RM = 100 × (1 + 5 ÷ 30) = 100 × 1.1667 = 116.7 kg.
- 3 Apply the Brzycki formula. 1RM = 100 × 36 ÷ (37 − 5) = 3,600 ÷ 32 = 112.5 kg.
- 4 Average the two estimates. (116.7 + 112.5) ÷ 2 = 114.6, so your estimated 1RM is about 115 kg.
- 5 Build your training weights. Multiply the 1RM by a percentage: 80% of 115 kg ≈ 92 kg for sets of about 8 reps.
Percentage of 1RM ↔ reps
Approximate reps most people can complete at each percentage of their one-rep max, shown here for a 1RM of 100 kg.
| % of 1RM | Reps | Weight (for a 100 kg 1RM) |
|---|---|---|
| 100% | 1 | 100 kg |
| 95% | 2 | 95 kg |
| 90% | 4 | 90 kg |
| 85% | 6 | 85 kg |
| 80% | 8 | 80 kg |
| 75% | 10 | 75 kg |
| 70% | 12 | 70 kg |
Reading and using the estimate
Treat the number as a well-informed projection, not a guarantee. The estimate is most reliable when it comes from a set of 1–10 reps taken close to failure; beyond that, muscular endurance and fatigue dominate, and both formulas tend to over-predict. If Epley and Brzycki disagree by a lot, that gap is a signal that your rep count was high — lean on the lower figure and re-test with a heavier, lower-rep set.
This tool is an informational estimate, not coaching or medical advice. A predicted 1RM is not a lift you are guaranteed to make. Warm up thoroughly, use safety pins or a spotter for heavy attempts, and progress gradually.