One Rep Max Calculator
Enter a completed set, choose an equation and compare its estimate with six other methods. The result is a prediction for that exercise; keep the movement and technique in view.
What an estimated 1RM means
A one-repetition maximum is the greatest load completed for one repetition of a particular exercise. An estimated 1RM uses a submaximal set to predict that number. The prediction depends on the equation and on how the set was performed; a comfortable warm-up set does not describe a repetition maximum.
The studies behind these methods used repetitions to fatigue or failure under defined test conditions. You can calculate from a set already in your log. The calculator does not require you to perform an unsupervised maximal or failure test. [1]
Keep the exercise and technique consistent
Enter a bench-press set to discuss your bench press, and a squat set to discuss that squat. Do the same for a deadlift. The arithmetic accepts these loads, but evidence from one lift does not establish equal accuracy for another. Ribeiro and colleagues studied bench press, squat and arm curl; that study did not validate a universal deadlift prediction. [2]
Record the exercise variation, load, repetitions and equation when comparing estimates over time. A change from a paused bench press to another setup needs context alongside the number.
Work through an 80 kg set of five
Using the Epley version in this calculator: 80 × (1 + 5 / 30) = 93.33 kg, displayed as 93.3 kg. The Brzycki version gives 80 × 36 / (37 − 5) = 90 kg. Neither number is a completed lift.
The difference is useful information. Keep the chosen method consistent instead of picking whichever result looks strongest. For percentages of a reference maximum, the 1RM percentage chart makes the arithmetic visible.
The seven formulas used here
w is the entered load, r is completed repetitions and e is the exponential constant. The output uses the same mass unit as the input. [1]
| Method | Calculation |
|---|---|
| Epley | w × (1 + r / 30) |
| Brzycki | 36w / (37 − r) |
| Lombardi | w × r^0.1 |
| Lander | w / (1.013 − 0.0267123r) |
| Mayhew | w / (0.522 + 0.419 × e^(−0.055r)) |
| O'Conner | w × (1 + 0.025r) |
| Wathen | w / (0.488 + 0.538 × e^(−0.075r)) |
Printed versions differ slightly. Whisenant's table prints 0.033 for Epley and rounded decimal coefficients for Brzycki; this site keeps its established r / 30 and 36 / (37 − r) versions and shows them explicitly. Lander, Lombardi, Mayhew, O'Conner and Wathen use the coefficients shown above. Small differences between calculators can therefore come from the implemented version and rounding. [1]
Read the result with its limits
Whisenant's study involved 69 collegiate male football players using a 225 lb bench-press test. Ribeiro's study involved 62 young women and 57 young men, with different findings by lift and sex. Those are study populations, not a promise that an equation fits every reader or exercise. [2]
The 1–10 repetition limit is this tool's chosen range. It does not make every estimate within that range accurate. A study of strength-endurance profiles also explains why repetition capacity can vary with the individual, exercise and training background. [3]
Do not treat a predicted number as an instruction to attempt it. For unfamiliar lifts or maximal testing, arrange qualified supervision and appropriate spotting. If you have a condition or injury affecting training, a calculator cannot decide which test is appropriate for you.
1RM questions
Does one completed rep prove my 1RM?
Only completing a single does not show that you could not lift more. This tool returns the entered single without inflating it, and labels it accordingly.
Can I enter kilograms or pounds?
Yes. Changing the unit converts the entered load and its input limits. Converted input values retain up to six decimal places; results display one decimal place.
Is 80% a recommended workout weight?
It is a percentage calculation. The appropriate load depends on your exercise, plan and ability to perform the work. The table does not prescribe sets or repetitions.
Sources
- Whisenant et al. (2003): Validation of submaximal prediction equations for the bench press — methods, equation table and supervised test context.
- Ribeiro et al. (2024): Accuracy of 1RM prediction equations in three lifts — equation coefficients, study population and exercise-specific findings.
- Mitter et al. (2022): Strength performance and strength-endurance profiles — individual variability and prediction limits.
- NIST Guide to the SI, footnote 22 — kilogram/pound conversion.