Slobiq Health / Training and fitness / One-rep max (1RM) calculator
One-rep max (1RM) calculator
Enter the weight you lifted and how many reps you did to estimate your one-rep max.
These are general estimates, not medical advice, and they do not replace a doctor, dietitian or trainer. If you are pregnant, under 18, have a health condition or take medication, talk to a professional before changing your diet or training.
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About this tool: One-rep max (1RM) calculator
Your one-rep max is the heaviest weight you can lift for a single repetition with good form. Testing it directly is tiring and risky without a spotter, so most people estimate it from a lighter set done close to failure.
The calculator shows two well-known formulas, Epley and Brzycki (1993), and the average of them. The estimate is most accurate for sets of 2 to 10 reps and gets less reliable above that. Use the percentages to pick training weights.
Formula
Epley: 1RM = weight × (1 + reps ÷ 30). Brzycki: 1RM = weight × 36 ÷ (37 − reps). The result is the average of the two. With one rep the 1RM equals the weight lifted.
Worked example
100 kg for 5 reps: Epley 116.7 kg, Brzycki 112.5 kg, average 114.6 kg. 80% of that is 91.7 kg and 90% is 103.1 kg.
Sources and accuracy
- Formulas and sources last reviewed
- Accuracy
- An estimate from published formulas. Real needs differ between people, so treat it as a starting point and adjust to how your body responds.
Sources and accuracy
Frequently asked questions
How accurate is a 1RM estimate?
Within a few percent for most people on common lifts, if the set was truly hard. Lifts and individuals differ, so test carefully before relying on it.
Is it safe to test my real 1RM?
Only with proper warm-up, a spotter or safety bars and good technique. For most training an estimate is enough.
Why only up to 15 reps?
Beyond about 10 to 15 reps, fatigue and endurance matter more than strength and the formulas become unreliable.