How to use the one rep max calculator
- Enter the weight you lifted and choose pounds or kilograms.
- Enter the number of whole reps you completed in a hard set. Estimates work best at 10 reps or fewer.
- Read the seven formula estimates side by side and the headline average.
- Use the percent table to see working weights at 50 to 100 percent of the estimate, rounded to loadable plate increments.
Formula
Epley: 1RM = w x (1 + r / 30)
Brzycki: 1RM = w x 36 / (37 - r)
Landers: 1RM = w / (1.013 - 0.0267123 x r)
Lombardi: 1RM = w x r^0.10
Mayhew: 1RM = w / (0.522 + 0.419 x e^(-0.055 r))
O'Conner: 1RM = w x (1 + 0.025 x r)
Wathen: 1RM = w / (0.488 + 0.538 x e^(-0.075 r))
In each formula w is the weight lifted and r is the number of reps. With one rep, the weight lifted is the one-rep max by definition. The seven estimates are averaged with equal weight for the headline value.
Worked example
Suppose you lift 100 lb for 5 reps. Epley gives 100 x (1 + 5/30) = 116.7, Brzycki gives 100 x 36/32 = 112.5, Landers gives 113.7, Lombardi 117.5, Mayhew 119.0, O'Conner 112.5 and Wathen 116.6.
The average of the seven is 115.5 lb, and the spread from lowest to highest is 112.5 to 119.0 lb.
At 90 percent of that average, a working weight is 103.9 lb, which rounds to 105 lb on a bar loaded in 5 lb steps.
Why seven formulas
Researchers have fitted many equations that predict a one-rep max from a submaximal set, and they were built on different lifters, exercises and rep ranges. Showing them together makes the uncertainty visible. When the formulas agree closely, you can be more comfortable with the number. When they spread widely, as they do above 10 reps, treat the estimate as a rough guide.
Getting a better estimate
Estimates are only as good as the set behind them.
- Use a set taken close to failure with strict form, not a set where you stopped with many reps in reserve.
- Use 2 to 6 reps when you can. Very high rep sets reflect endurance as much as strength.
- Use the same exercise and equipment you plan to test. A machine press and a barbell press are different tests.
- Treat the result as a planning number for training percentages, not a promise of what you can lift on a given day.
Safety
Testing a true one-rep max carries injury risk. Warm up, use safety pins or a spotter, and consider working from estimates instead. If you are new to lifting or have a medical condition, ask a qualified coach or health professional. For training pace and distance rather than weights, see the pace calculator.
Assumptions and limits
- Each formula is applied exactly as published. None is guaranteed to fit your body, lift or technique.
- The percent table uses the average estimate. The approximate reps column comes from the Epley relationship and is a model, not a prediction.
- Loadable weights assume 5 lb steps for pounds and 2.5 kg steps for kilograms. Your gym may use different plates.
- Reps must be whole numbers from 1 to 20, and accuracy falls off sharply above about 10.
- Information only. This is not coaching, medical advice or a guarantee of safety for any lift.
Frequently asked questions
Which one rep max formula is most accurate?
No formula wins for everyone. Epley and Brzycki are the most commonly used, and the others give similar values at low rep counts. That is why this page shows all seven and an average instead of picking one.
Why do the formulas disagree at high reps?
They were fitted to different data and they extrapolate differently. For example, the Brzycki formula divides by 37 minus the reps, so it rises steeply as reps climb, while Lombardi and O'Conner rise more slowly.
What does a percent of my 1RM mean for training?
Programs often prescribe sets at a percentage of the one-rep max, such as 80 percent for sets of a few reps. The percent table turns your estimate into those working weights so you do not have to do the arithmetic.
Can I enter one rep?
Yes. With one rep the weight you lifted is the one-rep max, so every formula returns it unchanged, and the page says so.
How accurate is a calculated one rep max compared with a real test?
It is an estimate and can be off by several percent, either way. A real maximal attempt is more direct, but it also carries more risk, so many lifters rely on estimates from near-maximal sets.