Health / 05
One-Rep Max Calculator (1RM)
Estimate the most you could lift once from a set of several reps, with seven published formulas side by side and a table of training loads by percentage, in kilograms or pounds.
One-Rep Max Calculator (1RM): The page applies the Epley, Brzycki, Lombardi, Mayhew, O'Conner, Wathen, and Lander formulas to your set and shows their average. The training table gives loads as percentages of that estimate, rounded to 2.5 kg or 5 lb, with the reps each roughly allows. Runs 100% locally in your browser with zero server file uploads.
- Category
- Health & sport tools
- Runs
- In your browser
- Cost
- Free · no sign-up
- Availability
- Ready to use
Runs entirely in your browser
An estimate from a set you can do safely, not a substitute for a supervised max attempt.
Why the formulas differ
Each formula was fitted to a different group of lifters and exercises. Epley adds a thirtieth of the weight for every rep; Brzycki divides by a factor that falls as the reps rise; others use exponential curves. For sets of up to about ten they agree within a few percent, so their average is a sensible single number, and the spread between them shows how uncertain the estimate is.
A set taken to genuine failure with good form gives the best estimate. Stopping with reps left in reserve makes the estimate too low, and sloppy reps make it too high.
Using the training table
The reps beside each percentage come from turning the Epley formula around: they are roughly how many reps that load allows, not a prescription. Strength work usually sits between about 80% and 90% for low reps; lighter loads for more reps build size and endurance. Loads are rounded to what a standard bar and plates can make.
For rest periods between sets, the interval timer counts work and rest; to estimate how much energy training adds to a day, see the calorie calculator.
How to use it
- Choose kilograms or pounds.
- Enter the weight and the reps you completed with good form.
- Read the estimate from each formula and the training loads from 50% to 100%.
Privacy & limitations
Everything is calculated in your browser. Nothing is stored except your choice of unit.
Related tools
Frequently asked questions
Which formula is the most accurate?
None is best for everyone. Epley and Brzycki, the most widely used, give the same result at 10 reps; below that, Epley reads slightly higher. The formulas were developed with experienced lifters, so beginners may find their true maximum lower.
How many reps should the set be?
Between about 3 and 10. With very few reps the estimate is close to what you lifted anyway; past 10 the formulas disagree more and more, because endurance starts to matter as much as strength.
Is it safe to test a real one-rep max?
A true max attempt carries more risk of injury, so it is best done with a spotter or a coach and after a proper warm-up. The point of an estimate is to plan training without one.
What are the percentages for?
Training programmes are often written as a percentage of your one-rep max, such as 5 sets of 5 at 80%. The table turns those percentages into loads for your estimate.
Free tool · runs in your browser · no account required