How the One Rep Max is Calculated

Have you ever wondered how your one rep max is calculated? Before creating Functional Strength Lab’s 1RM calculator, I asked the same question. I visited many sites to determine the math and reasoning behind the various calculations. Some of my findings were very interesting:

  1. There are seven distinct formulas that have been proposed to calculate 1RM’s. Two have become the industry standards: Epley & Brzycki. The five other calculations are slightly more complicated and are less recognized: Lander, Lombardi, Mayhew et al., O’Conner et al., & Wathan
  2. All calculations can be used interchangeably for all of the big three lifts: Bench Press, Squat, Dead Lift.
  3. All calculations require a weight that you can rep out for more than two reps, but less than 10-12 to remain fairly accurate.
  4. These calculations can help you avoid injuries that often result from actually performing your One Rep Max. While it’s difficult to refrain from “proving” your strength through one rep maxes, it seems pointless when you can craft your workouts using the fairly accurate figures that these calculations will spit out.


Various Calculations (where “r” stands for reps and “w” stands for weight used):

***Most Commonly Recognized 1RM Formulas***

Epley Formula

1RM = w \left ( 1 + \frac{r}{30}\right )


Bryzicki Formula1RM = w \cdot \frac {36}{ \left ( 37 - r \right ) } = \frac{w}{ \left [ \frac{37}{36} - \left ( \frac{1}{36} \cdot r \right ) \right ] } \approx \frac{w}{ \left [ 1.0278 - \left ( 0.0278 \cdot r \right ) \right ] }


***Less Recognized 1RM Formulas***


Lander Formula

1RM = \frac{100 \cdot w}{101.3 - 2.67123 \cdot r}


Lombardi Formula 

1RM = w \cdot r^{0.1}


Mayhew, et al.

1RM = \frac{100 \cdot w}{52.2 + 41.9 \cdot e^{-0.055 \cdot r} }


– O’Conner et al.

1RM = w \cdot (1 + 0.025 \cdot r)



1RM = \frac{100 \cdot w}{48.8 + 53.8 \cdot e^{-0.075 \cdot r}}


You can either crack open your notebook and start using these formulas yourself, or you can use these pre-crafted 1RM calculators created by Functional Strength Lab:

1RM Bench Calculator

1RM Squat Calculator

1RM Dead Lift Calculator

(Hint: As I’ve already mentioned, these are the same calculators!!!)

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