One Rep Max Calculator
This one rep max calculator estimates your 1RM from a lighter set, so you can skip the max test.
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Field Notes that go deeper
Keeping a log makes estimates like this easier to track. The GameLiftEat workout tracker is coming soon.
The science behind the one rep max calculator
Show the formulas, method and sources
A one-rep max, or 1RM, is the heaviest weight you can lift once with good form. The tool estimates it from a lighter set taken close to failure, using two common formulas, Epley and Brzycki.
Formulas
Epley
1RM = weight x (1 + reps / 30)For 1 rep, 1RM = weight
Brzycki
1RM = weight x 36 / (37 - reps)
Headline estimate
Estimate = average of the Epley and Brzycki results
How it works, step by step
- First, you enter the weight you lifted and the reps you completed, from 1 to 10.
- Then the calculator applies both formulas to the same set.
- Next, it averages the two results for your headline and also shows each formula on its own.
- Finally, it rounds weights to the nearest 0.5 kg or 1 lb.
Worked example
When someone lifts 100 kg for 5 reps, Epley gives 100 x (1 + 5/30) = 116.7 kg. Brzycki gives 100 x 36 / 32 = 112.5 kg. The average comes to 114.6 kg, which rounds to 114.5 kg at the nearest 0.5 kg.
Accuracy and limits
Reynolds, Gordon and Robergs tested lifts at 1, 5, 10 and 20 repetitions in 70 adults. They found that the 5-rep set predicted 1RM best, and they concluded that linear equations should use no more than 10 repetitions. For that reason, both formulas here carry a 10-rep limit.
The two formulas agree exactly at 10 reps. Below that, Epley gives a slightly higher estimate than Brzycki. In the same study, Epley's equation had small average errors on the leg press with a slight tendency to overestimate, while Brzycki's underestimated leg press strength.
Both formulas assume you took the set close to failure. If your set stopped well short, the estimate will come out too low.
- Results differ by exercise, and the study covered only a chest press and a leg press.
- An estimate guides tracking, so it does not tell you to load that weight on the bar.
- If you test heavy singles, use a spotter or safety arms, and warm up first.
Sources
- Reynolds JM, Gordon TJ, Robergs RA. Prediction of one repetition maximum strength from multiple repetition maximum testing and anthropometry. J Strength Cond Res. 2006;20(3):584-592. Used for: The Epley and Brzycki equations as written, their 10-rep guideline and how they compared.
Sources and math last reviewed: .
Questions people ask
What is the difference between Epley and Brzycki?
They are two ways to turn reps into an estimated max. Epley multiplies the weight by 1 plus reps divided by 30. Brzycki multiplies by 36 and divides by 37 minus reps. They give the same answer at 10 reps, and Epley reads a little higher below that.
How many reps should I use?
Use a set of 10 reps or fewer, taken close to failure. Research on these equations advises no more than 10 reps, and the 5-rep set predicted best of all. When you use higher reps, the estimate gets less reliable.
Is the 1RM calculator good for beginners?
It can be. Testing a true max takes practice and a spotter, so an estimate from a lighter set is a gentler route. If you keep the reps clean, you can use the number to track trends.
Can I use the result to pick my training weights?
Use it as a reference point, and start lighter while you learn the lift. Form matters more than the number, so add weight a little at a time and log what you lifted to see progress.
Why does my estimate change between exercises?
Researchers tested the formulas on only a small set of lifts, and accuracy differs by exercise. A bench press and a leg press can give different errors for the same person. If you compare estimates, compare the same lift over time.
These calculators give general estimates for adults and are not medical advice. For decisions about your own health, talk with a doctor or a registered dietitian. How we write and check things