One Rep Max (1RM) Calculator

Your one-rep max (1RM) is the maximum weight you can lift for exactly one complete repetition with proper form. Rather than risk injury testing it directly, most lifters estimate it from a submaximal set using a formula.

This calculator runs four of them and averages the result, because no single formula wins across every lift and rep range.

Epley

1RM = Weight × (1 + Reps / 30)

Brzycki

1RM = Weight × 36 / (37 − Reps)

Lombardi

1RM = Weight × Reps^0.10

Lander

1RM = 100 × Weight / (101.3 − 2.67123 × Reps)

Worked example

You squat 120 kg for 6 reps.

Average of the four: 141.9 kg, and that spread of about 5 kg between the highest and lowest is normal. Anyone quoting an estimated 1RM to a tenth of a kilo is overselling the arithmetic.

Epley reads highest and Brzycki lowest at 6 reps, and the gap between them widens as reps climb. At 10 reps Epley says 133% of your working weight and Brzycki says 133% too, but by 15 reps Epley is at 150% and Brzycki at 164%. That divergence is the honest signal that high-rep estimates are guesswork.

Training Percentages Based on 1RM:

1RM Standards by Lift (intermediate male lifter, ~80 kg bodyweight):

Practical Tips:

• Use sets of 3–5 reps for the most accurate 1RM estimates; accuracy drops significantly above 12 reps
• Retest every 6–8 weeks during a strength phase to keep training weights current
• The formula overestimates for very high rep sets (15+) because fatigue distorts the calculation

A fifth formula, for bench press only: Mayhew

The Mayhew formula was fitted specifically to bench-press data and tends to be the best predictor for that one lift:

1RM = 100 × Weight / (52.2 + 41.9 × e^(−0.055 × Reps))

On bench press it usually lands within 2 to 3% of a measured 1RM across the 3 to 10 rep range. It is deliberately left out of the average this calculator reports, because applying a bench-fitted curve to squats and deadlifts is not what it was built for. If you are testing bench specifically, run Mayhew by hand and give it more weight than the rest.

Safety: never test 1RM cold

Directly testing your 1RM carries real injury risk. The estimation formulas above let you skip that risk entirely. If you do test directly:

• Use a spotter, always. For squats and bench, two spotters is better than one.
• Thorough warm-up: 5–10 minutes general cardio, then warm-up sets at 50%, 70%, 85%, and 95% of estimated 1RM before attempting the test.
• Take 3–5 days of rest before a true 1RM test; testing fatigued risks both an inaccurate result and an injury.
• Set up safety pins or rails on a power rack to your dump position.
• Trust the estimation formulas if any of the above isn’t in place.