What is a one-rep max (1RM)?

A one-rep max (1RM) is the maximum amount of weight you can lift for a single repetition of an exercise with proper form. It is used as a reference point to set training loads at different percentages.

What formula is used to calculate 1RM?

Asterisks Fit uses the Epley formula: 1RM = weight × (1 + reps / 30). This is one of the most widely used estimation formulas and works best with sets of 1–10 repetitions.

Is it safe to test my actual one-rep max?

Testing a true 1RM carries injury risk and should only be done by experienced lifters with proper technique, an appropriate warm-up, and a spotter or safety equipment. Beginners should use submaximal rep testing with the estimation formula instead.

What percentage of my 1RM should I train at?

For hypertrophy (muscle size), 65–85% of 1RM for 6–15 reps is commonly recommended. For strength development, 80–95% for 1–5 reps. For muscular endurance, 50–65% for 15+ reps.

Free 1 Rep Max (1RM) Calculator

Your one-rep maximum (1RM) is the maximum weight you can lift for a single repetition of any exercise. This calculator uses the Epley formula to estimate your 1RM from a submaximal effort, so you never have to push to failure.

Calculate Your 1-Rep Max

Enter the weight you lifted and the number of reps you completed to estimate your 1RM.

Epley Formula Explained

1RM = Weight × (1 + (Reps ÷ 30))

Example: Squatting 100 kg for 5 reps → 1RM = 100 × (1 + (5 ÷ 30)) = 100 × 1.167 = 116.7 kg

The Epley formula is most accurate for 1–10 repetitions. Accuracy decreases at higher rep ranges (15+ reps).

Training Zones Explained

90–100% 1RM (1–3 reps)

Maximal strength. Develops neural drive and peak force production. Rest 3–5 min between sets.

75–85% 1RM (4–8 reps)

Strength and hypertrophy. Best for intermediate lifters building size and strength together.

65–75% 1RM (8–12 reps)

Hypertrophy. Classic muscle building rep range. Rest 1–2 min between sets.

50–65% 1RM (12–20 reps)

Muscular endurance. Higher volume, shorter rest periods. Great for conditioning.

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Frequently Asked Questions

Medical Disclaimer: 1RM estimates are for planning training loads. Do not attempt true 1RM testing without proper supervision and warm-up. Full disclaimer →