One Rep Max Calculator

Estimate the heaviest weight you could lift for one repetition — your one-rep max — from any lighter set, using the Epley and Brzycki formulas.

Your Estimated One Rep Max (Epley)

Health note: These are estimates, not measurements, and not medical advice — accuracy drops above about 10 reps. Never test a true one-rep max alone: use a spotter, warm up thoroughly, and stop if anything hurts. If you have a health condition or injury, talk to a qualified healthcare professional before heavy lifting.

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How It Works

Your one-rep max (1RM) is the heaviest weight you can lift once with good form. Testing it directly is risky, so lifters estimate it from a lighter set instead. Two formulas dominate: Epley, which gives weight × (1 + reps ÷ 30), and Brzycki, which gives weight × 36 ÷ (37 − reps). Both were developed from observed relationships between reps and maximum strength, and they usually agree within a few percent for sets of 10 or fewer reps.

The calculator shows both estimates plus their average, and a table of training percentages — 95% down to 50% of the Epley estimate — for planning strength, hypertrophy or endurance work.

Worked Example

Lifting 100 kg for 5 reps: Epley gives 100 × (1 + 5 ÷ 30) = 116.7 kg, and Brzycki gives 100 × 36 ÷ (37 − 5) = 112.5 kg — an average of 114.6 kg. At 90% of the Epley estimate you would train with about 105.0 kg, and at 70% with about 81.7 kg. Lifting 225 lb for 8 reps gives Epley 285.0 lb and Brzycki 279.3 lb.

How to Use This Calculator

Enter the weight you lifted and the number of reps you completed — ideally a set taken close to failure with 10 or fewer reps. You get the Epley and Brzycki estimates, their average, and a percentage table for planning training loads.

Tips and Practical Advice

Use a hard set for the input: a weight you could have lifted for five more reps tells the formulas almost nothing. The estimate is lift-specific — your squat 1RM says nothing about your bench press — so calculate each lift separately. And trust the bar over the formula: if 90% feels far too heavy or light in practice, adjust.

Sources: Epley formula (Epley, 1985); Brzycki formula (Brzycki, 1993). Reviewed Nov 13, 2026.

Frequently Asked Questions

Which formula is better, Epley or Brzycki?

Neither is clearly better — they usually land within a few percent of each other below 10 reps. Using the average of the two is a sensible middle ground.

Why do the formulas fail above 10 reps?

High-rep sets test muscular endurance more than maximum strength, so the link between reps and 1RM weakens. Above 10 reps the estimates drift and tend to overstate what you can lift once.

Last updated: November 2026