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.

1RM Calculator for Bench Press, Squat and Deadlift

Estimate your one-rep maximum (1RM) for key compound lifts. Choose between Bench Press, Squat, Deadlift, Overhead Press, or Barbell Row and compare four scientific lift equations.

Calculate Your 1-Rep Max

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

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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.

How the Calculation Works

Asterisks Fit strength predictions are based on established sports science load-velocity profiling equations:

Epley Formula (1985): Developed by strength coach Boyd Epley, this classic equation models strength endurance linearly:1RM = W × (1 + (R ÷ 30))Widely recognized as generally consistent for reps between 2 and 10 in major compound movements.
Brzycki Formula (1993): Formulated by Matt Brzycki, this equation is particularly accurate for predicting maximum strength in upper-body movements like the bench press:1RM = W ÷ (1.0278 − (0.0278 × R))
Safety of Submaximal Prediction: Peer-reviewed studies in sports medicine confirm that estimating 1RM from submaximal repetitions (e.g., a heavy set of 5 reps) provides a generally consistent metric for training program design while drastically reducing the risk of acute connective tissue or musculoskeletal injury.

Formula based on the published equation. Methodology reviewed by the Asterisks editorial team. Last content review: June 2025.

Last Updated: June 2026

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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 →