One Rep Max Calculator
Enter the weight you lifted, in pounds or kilograms, and how many clean reps you did, from 1 to 36. The calculator estimates your one-rep max (1RM) with four formulas, Epley, Brzycki, Lombardi and O'Conner, and shows all of them. Below them it lists 90%, 80%, 70% and 60% of the Epley estimate, rounded to whole pounds or kilograms, for setting working weights. Enter 1 rep and all four estimates equal the weight you lifted.
A whole number from 1 to 36.
How to use the One Rep Max Calculator
- Enter your numbers in the One Rep Max Calculator above.
- Press the Calculate 1RM button to see the result.
- To try other numbers, change any value and press the button again.
The 1RM formulas
Epley: 1RM = W × (1 + reps ÷ 30) · · · Brzycki: 1RM = W ÷ (1.0278 − 0.0278 × reps) · · · Lombardi: 1RM = W × reps^0.10 · · · O'Conner: 1RM = W × (1 + 0.025 × reps)
W is the weight lifted and reps is the number of clean reps. The formulas are as Wikipedia lists them in its one-repetition maximum article, and we did not read the original papers. The Brzycki line is a rounded form of W × 36 ÷ (37 − reps). Below 10 reps Epley gives the higher of the first two, the two nearly match at 10, and above that Brzycki climbs much faster. From 8 reps up, Lombardi and O'Conner stay below both. The calculator takes 1 to 36 reps, because from 37 reps the Brzycki divisor is 0 or less. Each figure is worked out on the weight as typed and rounded once, to whole pounds or kilograms.
Worked example
8 reps with 225 lb: Epley gives 225 × (1 + 8 ÷ 30) = 285 lb, and Brzycki gives 225 ÷ (1.0278 − 0.0278 × 8) = 279 lb. Lombardi gives 225 × 8^0.10 = 277 lb, and O'Conner gives 225 × (1 + 0.025 × 8) = 270 lb. The percentage row, worked from the Epley number, shows 257, 228, 200 and 171 lb for 90%, 80%, 70% and 60%.
Frequently asked questions
How many reps can I enter?
Any whole number from 1 to 36. One rep returns the weight you lifted. Up to 10 reps the Epley and Brzycki estimates stay within 4% of each other. Above that they drift apart, and at 20 reps Brzycki is 27% higher than Epley.
Why do the formulas disagree?
They bend differently as the reps go up. For 225 lb × 5 the calculator shows 263 lb by Epley, 253 lb by Brzycki, 264 lb by Lombardi and 253 lb by O'Conner. At 10 reps on a 100 lb lift, Epley and Brzycki are within a pound of each other, with Lombardi at 126 lb and O'Conner at 125 lb. At 20 reps Brzycki is 45 lb higher than Epley.
What are the Lombardi and O'Conner formulas?
Lombardi multiplies the weight by the reps raised to the power 0.10. O'Conner adds 2.5% of the weight for each rep. Both are listed with the others in Wikipedia's one-repetition maximum article. For 20 reps at 100 lb they give 135 lb and 150 lb, while Epley gives 167 lb and Brzycki 212 lb.
Which formula should I trust?
This page cannot pick one for you, and no figure here is a tested maximum. The Wikipedia article says the estimate may not be accurate and can be a starting point for a real 1RM test. If your program is written around one formula, use that one. A set of a few reps brings the four closer together. At 3 reps with 225 lb they run from 238 lb to 251 lb.
How do I use the percentage row?
It lists 90%, 80%, 70% and 60% of your Epley estimate, so you can read off working weights without a second calculation. Heavier percentages go with fewer reps per set. Round each load to the plates you have.