How one rep max calculator works
Your one-rep max (1RM) is the heaviest weight you can lift for a single repetition with good form. Testing a true 1RM is risky and tiring, so it is usually estimated from a lighter weight you lift for several reps. Enter the weight and the reps you performed, pick a formula, and the tool estimates your 1RM.
Four formulas are supported. Epley (1RM = weight x (1 + reps/30)) is the most common and works well for 1-10 reps. Brzycki (1RM = weight x 36 / (37 - reps)) is similar and preferred for low reps. Lombardi (1RM = weight x reps^0.10) and Lander are alternatives. The tool shows the result of the chosen formula plus all four estimates so you can compare.
The tool also builds a percentage-of-1RM training table using the Brzycki inverse relationship (percent = (37 - reps) / 36), so you can see the load that corresponds to each rep target (1, 2, 3, 4, 5, 6, 8, 10, 12 and 15 reps). For example, a load you can lift for 8 reps is roughly 80% of your 1RM. Estimates grow unreliable above about 10 reps and are for education only, not medical or coaching advice.
Frequently asked questions
Which 1RM formula is most accurate?
Epley and Brzycki are the most studied and widely used, and give very similar results for 1-10 reps. Brzycki is often preferred for low rep ranges (1-6), while Epley handles slightly higher reps a little better. Comparing all four formulas in the results lets you see the spread and pick a sensible middle estimate.
How many reps should I use for the estimate?
Use the heaviest weight you can lift for 1-10 reps with clean form. The closer your test set is to 1 rep, the more accurate the estimate. Above about 10 reps the formulas become unreliable because they extrapolate far beyond the data they were built from, so keep test sets under 10 reps when possible.
What is the percentage-of-1RM training table for?
It shows the load that corresponds to each rep target (for example, 8 reps at about 80% of your 1RM, or 5 reps at about 86%). Strength programs are written as percentages of 1RM, so the table helps you turn a single max estimate into actual weights to put on the bar for each set.
Is this one rep max estimate safe to test?
The formula estimate is safer than a true 1RM test because it uses a submaximal weight. Still, only lift weights you are trained to handle, use a spotter or safety pins for free-weight lifts, and warm up thoroughly. If you are new to resistance training or have any health concerns, work with a qualified coach or consult a doctor before maxing out.
