One-Rep Max Calculator
Enter weight and reps to instantly estimate your one-rep max with two proven formulas.
How one-rep max formulas work
The one-rep max (1RM) is the maximum weight you can lift for a single repetition of a given exercise. Because testing your true 1RM can be dangerous, two widely used formulas let you estimate it from a submaximal set. The Epley formula (weight multiplied by one plus reps divided by 30) tends to be slightly more generous at higher rep ranges. The Brzycki formula (weight multiplied by 36, divided by 37 minus reps) is undefined for 37 or more reps and converges more closely with Epley at lower rep counts. Both formulas are unit-agnostic: enter your weight in kilograms or pounds and the result is in the same unit. All calculations run entirely in your browser and nothing is sent to a server.
The percentage table shows how much weight corresponds to each intensity level from 60 to 100 percent of your estimated 1RM. Coaches commonly use these percentages to prescribe training loads: 85 to 95 percent for strength work, 70 to 85 percent for hypertrophy, and 60 to 70 percent for muscular endurance. Treat the estimates as a starting point and adjust based on how you feel on a given day.
FAQ
Which formula should I trust? Both are reasonable estimates. The Epley formula is slightly more commonly cited and works for any number of reps above zero. Brzycki is only defined for up to 36 reps. If your set is 10 reps or fewer the two formulas give very similar results; for higher rep sets they can diverge more.
Is my data stored anywhere? No. All calculation happens client-side in JavaScript. Nothing is uploaded or logged.