One Rep Max Calculator: 1RM by 7 Formulas + % Table
Estimate your one-rep max from a weight and 1 to 12 reps with the Epley, Brzycki, Lander, Lombardi, Mayhew, O'Conner and Wathan equations side by side, their average, and a 50 to 100 percent training table. Kilograms or pounds. Nothing is sent.
Enter the weight you lifted and how many reps you managed.
About the One Rep Max Calculator
The One Rep Max Calculator estimates your one-repetition maximum, or 1RM: the heaviest weight you could lift once with good form. Instead of testing a true maximum, you enter a lighter weight you lifted and how many clean reps you managed, from 1 to 12. The page then applies seven published prediction equations side by side, Epley, Brzycki, Lander, Lombardi, Mayhew, O'Conner and Wathan, and shows their average.
Below the estimates a percentage table lists training loads from 100 percent of your 1RM down to 50 percent in 5 percent steps, each with the number of reps you could expect to manage at that load. Coaches use these percentages to set the weight for strength, hypertrophy and endurance work. You can work in kilograms or pounds; every equation is proportional to the weight, so the unit does not change the result.
This is an estimate, not medical advice. Attempt a true one-rep max only with good technique, a proper warm-up and a spotter.
How to estimate your 1RM
Steps
- Choose kilograms or pounds.
- Enter the weight you lifted and the number of full reps you completed before form broke down.
- Read the average estimate, compare the seven equations, and use the percentage table to pick training loads.
Best rep range
The equations are most accurate between about 2 and 10 reps. Above 10 reps the estimates drift apart, because endurance starts to limit the set more than strength, so the page shows a warning. With a single rep, the weight you lifted already is your one-rep max.
The equations
With w the weight lifted and r the reps completed:
The rep counts in the percentage table come from the Epley equation solved for reps, r = 30 × (1RM ÷ load − 1), rounded to the nearest whole rep.
Worked example
Lifting 100 kg for 5 reps gives 116.7 kg by Epley, 112.5 kg by Brzycki, 113.7 kg by Lander, 117.5 kg by Lombardi, 119.0 kg by Mayhew, 112.5 kg by O'Conner and 116.6 kg by Wathan. The average is 115.5 kg, so 80 percent of it, about 92.4 kg, is a load you could lift for around 8 reps.
Why the equations differ
Each equation was fitted to a different group of lifters and exercises, such as the bench press or the squat, so none is right for everyone. Brzycki and O'Conner tend to give the lowest estimates for higher reps and Mayhew and Lombardi the highest. The average smooths out these differences, which is why it is shown first.
Privacy
Nothing is uploaded; the calculation runs in your browser and never leaves your device.
Related tools
Convert between kilograms and pounds with the Mass Converter, estimate the energy your training uses with the Calories Burned Calculator, or check your weight against your height with the BMI Calculator.
Sources
- Epley B. Poundage chart. Boyd Epley Workout. Lincoln, NE: Body Enterprises; 1985.
- Brzycki M. Strength testing: predicting a one-rep max from reps-to-fatigue. Journal of Physical Education, Recreation & Dance 1993;64(1):88–90.
- Lander J. Maximums based on reps. National Strength and Conditioning Association Journal 1985;6:60–61.
- Lombardi VP. Beginning weight training. Dubuque, IA: W.C. Brown; 1989.
- Mayhew JL, Ball TE, Arnold MD, Bowen JC. Relative muscular endurance performance as a predictor of bench press strength in college men and women. Journal of Applied Sport Science Research 1992;6(4):200–206.
- O'Conner B, Simmons J, O'Shea P. Weight training today. St. Paul, MN: West Publishing; 1989.
- Wathan D. Load assignment. In: Baechle TR, ed. Essentials of strength training and conditioning. Champaign, IL: Human Kinetics; 1994:435–446.
- LeSuer DA, McCormick JH, Mayhew JL, Wasserstein RL, Arnold MD. The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift. Journal of Strength and Conditioning Research 1997;11(4):211–213.
Open-source credits
The calculations are implemented in-house in TypeScript. They follow the published Epley, Brzycki, Lander, Lombardi, Mayhew, O'Conner and Wathan equations, and no third-party code is used.
Frequently asked questions
What is a one-rep max?
Your one-rep max, or 1RM, is the heaviest weight you can lift once with good form for a given exercise. Training programmes often set loads as a percentage of it, such as 80 percent for sets of about eight reps.
Which 1RM formula is the most accurate?
None is best for everyone. Each equation was fitted to different lifters and exercises, and studies find they agree closely at low reps and drift apart above about 10. The page shows all seven, Epley, Brzycki, Lander, Lombardi, Mayhew, O'Conner and Wathan, and uses their average for the percentage table.
How many reps should I use for the estimate?
A set of 2 to 10 reps taken close to failure gives the most reliable estimate. The page accepts up to 12 reps but warns that accuracy falls above 10, because endurance starts to limit the set more than strength.
How are the reps in the percentage table worked out?
They come from the Epley equation solved for reps: reps = 30 × (1RM ÷ load − 1), rounded to the nearest whole rep. At 80 percent of your 1RM that gives about 8 reps, and at 50 percent about 30.
Does the unit change the result?
No. Every equation scales in proportion to the weight lifted, so the estimate is the same whether you work in kilograms or pounds; the page only converts for display.