Your one-rep max (1RM) is the heaviest weight you can lift for a single, correct repetition. Testing it directly is hard on the body and risky without help, so this free calculator estimates it from a lighter set. Enter the weight you lifted and the number of reps you completed, and you will get three estimates, their average and a percentage chart you can train with.
The three formulas
Researchers have published many equations. This calculator uses three well-known ones, where w is the weight lifted and r is the number of reps:
| Formula | Equation |
|---|---|
| Epley | w × (1 + r ÷ 30) |
| Brzycki | w × 36 ÷ (37 − r) |
| Lombardi | w × r0.10 |
For example, lifting 100 kg for 5 reps gives Epley 116.7 kg, Brzycki 112.5 kg and Lombardi 117.5 kg. The average is about 115.5 kg, which the calculator rounds to the nearest 0.5 kg (or the nearest pound in US units). If you lifted the weight for only one rep, that weight is your max.
How accurate is it?
The estimates are best when you use a set of about 2 to 8 reps taken close to failure with good form. Accuracy drops as reps rise: above 10 reps the formulas can be well off, and the calculator will warn you. The exercise, your training experience and your fitness also change the result, so treat it as a guide, not a promise.
Training percentages
| Percent of 1RM | About how many reps | Typical use |
|---|---|---|
| 100% | 1 | Maximum strength test |
| 95% | 2 | Heavy strength work |
| 90% | 4 | Strength |
| 85% | 6 | Strength |
| 80% | 8 | Strength and muscle growth |
| 75% | 10 | Muscle growth |
| 70% | 12 | Muscle growth and endurance |
| 65% | 15 | Endurance and warm-up sets |
Lift safely
- Warm up with light sets first. A short stretching routine helps you move well.
- Use a spotter or safety bars for squats and bench press.
- Do not test a true one-rep max alone. An estimate from a lighter set is a safer way to track progress.
- Stop if you feel sharp pain, dizziness or chest discomfort.
New to lifting? Our guide to strength training basics for beginners at home explains how to start. Support muscle with enough protein using the protein calculator, and track your body composition with the body fat calculator.
Check with a professional first if…
- You have heart disease, high blood pressure or a joint, back or shoulder injury.
- You are pregnant or recovering from surgery.
- You are new to heavy lifting. A qualified coach can teach safe technique.
Frequently asked questions
What is a one-rep max?
It is the most weight you can lift for one full repetition of an exercise with good form. It is used to set training weights as a percentage of your max.
Which one-rep max formula is the most accurate?
None is best for everyone. Epley, Brzycki and Lombardi often differ by a few percent, so the calculator shows all three and their average. Brzycki tends to rise fastest at higher rep counts.
Why does accuracy drop above 10 reps?
Long sets depend more on endurance than on maximum strength, and fatigue differs from person to person. For a better estimate, use a heavier set of 3 to 8 reps.
Should I test my real one-rep max?
It is not needed for most people. If you do, warm up well, use a spotter or safety bars, and never do it alone.
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This calculator provides general estimates for healthy adults and is for information only. It is not medical advice and does not replace a conversation with a qualified healthcare professional. Read our disclaimer and editorial policy.