One Repetition Maximum (1RM) Calculator

Calculate Your One Repetition Maximum (1RM)

Instructions: To calculate the maximum amount of weight that you can lift just once (also known as your "one repetition maximum" or "1RM") for any given type of weight lifting exercise, select a weight that you predict you can lift up to a maximum of 10 repetitions and perform a set with this chosen weight, completing as many repetitions as you can until failure (i.e. continue lifting until you can no longer lift the weight with proper form). If you exceed 10 repetitions before failure then, after resting for 10 minutes, try a heavier weight such that you fail before or at 10 repetitions. When you are finished enter the amount of weight you lifted and the number of repetitions you completed into the 1RM calculator below.

Weight Lifted

Repetitions Completed

Note: This 1RM calculator is considered to be reasonably accurate for entries of up to 10 repetitions. The calculator will not determine your 1RM for repetition values greater than 10. Also note that this 1RM calculator should be treated only as a rough prediction tool, and its accuracy will vary depending on a large number of factors, one of which is the resistance training experience of the user. In general, a 1RM calculator will return more accurate results for an experienced weightlifter.

About This Calculator

This 1RM (one repetition maximum) calculator provides estimates, according to seven different formulas, of the maximum amount of weight you would be able to lift only once for any given resistance exercise. Although it is possible to determine your 1RM through trial and error, it is generally not advisable for safety reasons. If you want to know the heaviest weight you would be able to lift for a given exercise, a 1RM calculator is a safe and reliable alternative to an actual attempt of a maximum lift. Note that you can use this 1RM calculator for any type of lift. There is no specific 1RM formula for deadlift, squat, bench press, etc. This calculator accurately determines your 1RM for any and all resistance exercises.

Calculator Reliability

How reliable are the estimates of a 1RM calculator? Well, the 1RM calculator formulas used for the calculator above have been experimentally shown to predict 1RM to within roughly 5% of actual achieved 1RM values for both bench press and squat, and to within roughly 10% of actual achieved 1RM values for deadlift.

Calculator Formulas

This 1RM calculator returns predictions of 1RM for the seven different formulas described below:

Brzycki: 1RM = W x (36 / (37 - R))
Epley: 1RM = W x (1 + 0.0333 x R)
Lander: 1RM = (100 x W) / (101.3 - 2.67123 x R)
Lombardi: 1RM = W x R^0.1
Mayhew et al.: 1RM = (100 x W) / (52.2 + (41.9 x e^{-0.055 x R}))
O'Conner et al.: 1RM = W x (1 + 0.025 x R)
Wathan: 1RM = (100 x W) / (48.8 + (53.8 x e^{-0.075 x R}))

where

1RM = One Repetition Maximum

W = Weight Lifted

R = Repetitions Completed

e = Euler's Number = 2.71828 (approximately)

References

LeSuer DA, McCormick JH, Mayhew JL, Wasserstein RL, Arnold MD. The accuracy of prediction equations for estimating 1RM performance in the bench press, squat, and deadlift. J Strength Cond Res. 1997. 11(4):211-13.