About the 1RM Calculator
What is the 1RM Calculator?
Your one-rep max (1RM) is the heaviest weight you can lift once with good form. Testing it directly is risky, so this 1RM calculator estimates it from a set of several reps.
It also builds a table of training weights for different rep ranges, so you can plan strength and hypertrophy sessions.
How to use the 1RM Calculator
- Weight Lifted (kg) (sample: 80)
- Repetitions Completed (sample: 8)
- Press Estimate One-Rep Max (results also refresh as you type). The result card shows the Estimated 1RM, along with Brzycki formula, Lombardi formula and Accuracy.
Formula used
Epley: 1RM = Weight × (1 + Reps ÷ 30)
- Brzycki = weight × 36 ÷ (37 − reps)
- Lombardi = weight × reps^0.1
Estimates are most reliable from sets of 10 reps or fewer taken close to failure.
Worked example
These are the sample values already filled in the calculator above, and the result it returns for them:
| Input | Sample value |
|---|---|
| Weight Lifted (kg) | 80 |
| Repetitions Completed | 8 |
| Result | Value |
|---|---|
| Estimated 1RM | 101.3 kg |
| Brzycki formula | 99.3 kg |
| Lombardi formula | 98.5 kg |
| Accuracy | Good – estimates are most reliable at 10 reps or fewer |
Tips for using the 1RM Calculator
- Train strength at 80–90% of 1RM (3–6 reps) and muscle size at 65–80% (8–12 reps).
- Re-estimate every 4–6 weeks as you get stronger.