This all-in-one online One Rep Max Calculator estimates the one-rep max from a given amount of repetitions at another weight. The one-rep max (one repetition maximum or 1RM) is the maximum amount of weight one can lift in a single repetition for a given exercise. Choose one of the several common formulas used to estimate 1RM. Then enter the values of any two known parameters in the fields of this online calculator and find the missing one.
Calculating one rep max
One-repetition maximum (one rep max or 1RM) in weight training is the maximum amount of weight that a person can possibly lift for one repetition. It’s essentially a prediction of a person’s best lift from a sub-maximal effort. One rep max can be used for determining a person’s maximum strength and also can be used as an upper limit when determining the desired load for an exercise (as a percentage of the 1RM) which is preferable instead of trying to do a 1RM attempt.
Determining the 1RM can be done directly through trial and error or using a one rep max calculator. There are a number of common formulas used to estimate the one-repetition maximum using the sub-maximal method. Our online 1RM calculator uses the formulas shown bellow, where \(r\) is the number of repetitions performed and \(w\) is the weight used (note that \(w\) is proportional to \(1RM\), so the unit of weight measurement doesn’t matter).
Brzycki
$$1\text{ RM} = \frac {36w}{37 – r} \approx \frac w {1.0278 – 0.0278r}$$
Epley
$$1\text{ RM} = w \left ( 1+ \frac r {30}\right )$$
Lander, McGlothin
$$1\text{ RM} = \frac{100w}{101.3 – 2.67123r}$$
Lombardi
$$1\text{ RM}= w r^{0.10}$$
Mayhew et al.
$$1\text{ RM} = \frac{100w}{52.2 + 41.9e^{-0.055r}}$$
O’Conner et al.
$$1\text{ RM} = w \left(1 + \frac r {40} \right)$$
Wathen
$$1\text{ RM} = \frac{100w}{48.8 + 53.8e^{-0.075r}}$$
The Brzycki and the Epley formulas are the most popular ones, while Epley seems to be better suited for low rep people.
The degree of accuracy of these formulas can vary largely depending on the weight training experience and muscular composition of the athlete. But they do a reasonably good job for up to 10 reps. Anyway it’s worth trying this 1RM calculator to see what formula works best for you.
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Disclaimer. Information provided here is for educational purposes only. Any suggestions given are in no way intended to be a substitute for professional advice. Our website assumes no responsibility for personal injury or damage sustained by or through the use of any advice given.