Fitness
One-Rep Max Calculator
Enter the weight you lifted and the reps you completed to estimate your one-rep max using both the Epley and Brzycki formulas.
Calculation inputs
Estimates are most accurate for sets of 10 reps or fewer.
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Estimates only, for general information. Not medical or training advice.
About this calculator
A one-rep max calculator estimates the heaviest weight you could lift for a single repetition, based on a lighter weight lifted for multiple reps. Lifters and coaches use it to set training percentages without needing to test a true maximum lift.
How the calculation works
- Epley: 1RM = weight × (1 + reps ÷ 30)
- Brzycki: 1RM = weight × 36 ÷ (37 − reps)
- The headline figure averages the two formulas
Notes and assumptions
Accuracy falls off above about 10 reps, where the formulas start to overestimate.
Always work up with a spotter before testing a true one-rep max.
How it works in plain English
Because lifting a submaximal weight for multiple reps correlates fairly closely with a true one-rep max, several formulas have been developed to estimate it from a single set. Two of the most common are the Epley formula and the Brzycki formula, which take the weight lifted and the number of reps completed and produce an estimated maximum.
These formulas tend to agree closely for sets of about 10 reps or fewer, which is why most calculators note that accuracy declines for higher rep counts. At higher reps, muscular endurance starts to influence the result more than raw strength, making the estimate less reliable.
Once an estimated max is calculated, it's common to build a table of training percentages, such as 70% or 85% of that number, to guide how much weight to use for different rep ranges in a program. This is why many one-rep max tools also display a percentage breakdown alongside the estimate.
The formula
- Epley: 1RM = weight x (1 + reps / 30)
- Brzycki: 1RM = weight x 36 / (37 - reps)
Worked example
Suppose someone lifts 225 pounds for 5 reps. Using the Epley formula, 225 x (1 + 5/30) = 225 x 1.167 = about 262.5 pounds. Using the Brzycki formula, 225 x 36 / (37 - 5) = 225 x 36 / 32 = about 253 pounds.
The two formulas differ by roughly 9 pounds in this case, which is typical, so many people average the two results, landing on an estimated one-rep max of about 258 pounds for planning purposes.
From that 258-pound estimate, a training table can be built directly: 90% would be about 232 pounds for very heavy singles or doubles, 80% would be about 206 pounds for sets of 4 to 6 reps, and 70% would be about 181 pounds for sets of 7 to 10 reps. Rounding these numbers to the nearest 5 pounds makes them easier to load on a barbell in practice, and most lifters revisit the estimate every few months as strength changes.
Common training percentages of estimated 1RM
| % of 1RM | Typical rep range |
|---|---|
| 90-100% | 1-3 reps |
| 80-89% | 4-6 reps |
| 70-79% | 7-10 reps |
| 60-69% | 11-15 reps |
| Below 60% | 15+ reps |
Percentage ranges reflect widely used strength-training guidelines and vary by program and individual.
Frequently asked questions
How accurate is an estimated one-rep max?
It's generally a reasonable approximation, especially for sets of 10 reps or fewer, but it can be off by several pounds either way depending on individual fatigue resistance, lifting experience, and the exercise being tested.
Why do different formulas give different results?
Each formula was derived from different sets of lifting data and makes slightly different assumptions about how strength declines as reps increase. None is universally more accurate; most people average two or more estimates for a middle-ground figure.
Should I test my actual one-rep max instead?
A true test gives an exact number but carries more fatigue and injury risk, particularly for less experienced lifters. Estimating from a submaximal set is a lower-risk way to get a working number for programming.
Does this work for any exercise?
The formulas were developed mainly using barbell exercises like the squat, bench press, and deadlift. They tend to be less reliable for exercises involving smaller muscle groups or more technical stabilization, such as overhead or single-limb movements.
Why does accuracy drop at higher rep counts?
At higher reps, factors like muscular endurance and pacing start to matter more than the raw strength being measured, so the mathematical relationship between weight and reps becomes less consistent, widening the margin of error.