Training6 min readCalcFitLab Editorial TeamUpdated 2026-08-19

What Is 1RM? How to Calculate Your One-Rep Max

1RM sits at the heart of any strength program. Here is how to estimate it safely and use the percentages in your training.

Calculate it for yourself

One-Rep Max Calculator

Estimate your 1RM from a set, with a % loading table.

The one-rep max, or 1RM, is the heaviest weight you can lift for a single clean rep. It is the base unit of strength. Training percentages are built from it, progress is compared to it and load is planned around it. The catch is that testing a true 1RM is risky.

Why 1RM is better estimated

A maximal single carries a higher injury risk, especially without a spotter. So most lifters estimate 1RM from a normal set taken close to failure. It is safer and accurate enough for planning.

Two working formulas

1RM = weight x (1 + reps/30)

Epley formula (1985), one of the most common one-rep-max estimates.

Epley, Boyd (1985)

1RM = weight x 36 / (37 - reps)

Brzycki formula (1993). Close to Epley at low reps and diverges at high reps.

Brzycki, Matt (1993)

For example, if you lifted 100 kg for 5 reps, Epley gives 100 x (1 + 5/30), about 117 kg. Brzycki gives 100 x 36 / 32, about 112 kg. Use them as a range, not one exact figure.

How to use 1RM percentages

About 85 percent of 1RM is roughly 6 reps.
About 75 percent is roughly 10 reps.
About 90 percent is roughly 4 reps.

Frequently asked questions

Neither is universally better. At low reps they nearly match, and at high reps Epley usually gives a bit more. Using both gives a sensible range instead of a single point.

Between 2 and 10 reps close to failure. Single sets and very high-rep sets make the estimate less reliable.

Yes. Attempting a true 1RM carries more injury risk, especially without a spotter. Estimating from a moderate set avoids the maximal load and still sets your training percentages.

The Epley formula estimates your one-rep max as weight times (1 plus reps divided by 30). For example, lifting 100 kg for 5 reps gives about 117 kg. The Brzycki formula is a common alternative and is slightly more accurate at low rep counts. Both are most reliable when your test set is under about 10 reps.