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One Rep Max (1RM) Calculator

Enter the weight you lifted and the number of reps; using the Epley formula we estimate your one-rep max (1RM) and your 90%, 80% and 70% training loads.

Estimated with the Epley formula: 1RM = weight × (1 + reps/30). Actual max varies by individual.

How it is calculated

The one-rep max (1RM) is the heaviest weight you could lift for a single repetition. Testing it directly is risky, so the tool estimates it from a set you have already done using the Epley formula: 1RM = w × (1 + reps / 30), where w is the weight lifted in kilograms and reps is the number of clean repetitions. A set of one rep simply returns the weight itself. The reps are rounded to a whole number and must be at least 1. The tool also lists 90%, 80% and 70% of the estimate, which are common training percentages. Epley is most reliable for sets of about 2 to 10 reps; at very high reps the estimate becomes optimistic and varies by exercise and by person.

Worked example

You squat 80 kg for 5 clean reps. Step 1: reps / 30 = 5 / 30 = 0.1667. Step 2: 80 × (1 + 0.1667) = 93.33 kg as the estimated one-rep max. Training weights follow from it: 90% is 84.00 kg, 80% is 74.67 kg and 70% is 65.33 kg. Treat 93.33 kg as a planning number rather than a promise that you can lift it on any given day.

Try this example →

Common mistakes

  • Counting reps that were grinding or partial; the formula assumes every rep was a full, controlled repetition.
  • Using a set of 15 or 20 reps, where the estimate overshoots and is much less accurate than from a heavy set of 3 to 5.
  • Entering pounds when the result is labelled in kilograms.
  • Applying a single estimate to every lift; the same formula is more accurate for some exercises than others, and your real max on a bad day will be lower.
  • Loading the bar to the estimated 1RM without a spotter or proper warm-up.

About this calculator

This calculator estimates the maximum weight you could lift for a single repetition — your one-rep max (1RM) — from the weight and rep count of a set you actually completed, using the Epley formula. Since testing a true 1RM directly carries injury risk, especially for lifts like the bench press or squat, lifters instead lift a submaximal weight for several reps and let the formula extrapolate the theoretical max.

Strength trainers use the result to program percentage-based training, where a set is prescribed as, say, 80% of 1RM rather than a fixed number of kilograms; the calculator also outputs 90%, 80% and 70% loads directly so a lifting program's target weights can be set without extra math.

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