One Rm
One Rm — runs in your browser. Inputs are not stored.
1RM estimate
Enter values, then press Calculate.
Estimated formula. Error can be large for high reps or beginners.
How to use
- Enter the weight (kg) you actually lifted. The default example is 60.
- Enter the reps performed at that weight. The default is 5. If it was 1 rep, that weight is already 1RM.
- Press Calculate to see Epley and Brzycki estimates side by side.
- High reps (about 12 or more) increase error. Test a true 1RM only with a spotter and safely.
- Reset restores 60 kg and 5 reps. The unit is kg.
Key concepts
The 1RM calculator estimates bench-press or squat max from reps. Epley is weight × (1 + reps/30); Brzycki is weight × 36 / (37 − reps). If the two values differ, use the more conservative one or an average. Assumptions fit low-rep work better. If the formulas split, treat the lower number as that day’s ceiling and warm up thoroughly. Do not confuse a high-rep estimate with a measured 1RM.
At 37 reps or more the Brzycki denominator breaks and that field may be blank. Beginners, machines, and partial reps differ from the formulas’ assumptions. Warm up with less than the estimate to reduce injury risk. High reps are muscular endurance, so error is large. Do not attempt a real 1RM without a spotter and a warm-up. Measured 1RM has injury risk—start below the estimate.
Example
60 kg for 5 reps: Epley is 60 × (1 + 5/30) = 70.0 kg; Brzycki is 60 × 36 / 32 = 67.5 kg. 80 kg for 3 reps is Epley 88 kg and Brzycki about 84.7 kg. Entering 1 rep at 80 kg shows 80.0 kg in both fields. 100 kg for 2 reps is Epley about 106.7 kg and Brzycki about 105.9 kg. At 37+ reps the Brzycki field may be empty. 70 kg for 8 reps is Epley about 88.7 kg and Brzycki about 86.9 kg. You can treat the lower of the two as a reference.
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Frequently asked questions
What happens in the 1RM calculator if I enter 1 rep?
The entered weight is treated as 1RM and both formulas show the same number. Both fields match the input weight.
Which 1RM is correct, Epley or Brzycki?
Both are estimates—use an average or the conservative figure. The gap grows with higher reps. If they split, using the lower as a warm-up ceiling is safer.
Are 1RM inputs sent to a server?
No. Calculation stays in the browser. Weight is not transmitted.
What about injury risk on a real 1RM test?
The formulas are a reference. Measure only with a warm-up and a spotter. Start below the estimate; do not test without a spot.
Is the 1RM unit pounds?
It is kg. Convert from pounds before entering. The unit is kg.
Why is error large with many reps?
The formulas assume low-rep strength. 15–20 reps is muscular endurance and sits far from max force. Reliability drops at 15+ reps.
Last reviewed: 2026-09-04