Quick answer
One rep max (1RM) is estimated from a lift of several reps. Epley: 1RM = weight × (1 + reps ÷ 30). Brzycki: 1RM = weight × 36 ÷ (37 − reps). Lifting 100 for 5 reps gives about 116.7 (Epley) or 112.5 (Brzycki).
Enter the weight lifted and the repetitions. The calculator returns estimates from both formulas.
Related tools: Training Load Calculator: Session load from perceived exertion and duration. Workout Volume Calculator: Total lifted volume from sets, reps and weight. Pace Calculator: Pace and speed from a distance and a time.
How to use the One Rep Max Calculator
- Enter weight lifted (above 0).
- Enter repetitions (a whole number, between 1 and 30).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Weight lifted | A number | > 0 |
| Repetitions | A whole number | ≥ 1, ≤ 30 |
Formula and method
Formula
Epley: 1RM = w × (1 + reps ÷ 30); Brzycki: 1RM = w × 36 ÷ (37 − reps)
IEEE-754 double precision; shown to 1 decimal place unless stated.
Both formulas are least accurate above about 10 repetitions. Use with caution and proper spotting. Informational estimate, not medical advice. Talk to a qualified health professional about your own situation.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Weight lifted = 100; Repetitions = 5.
| Result | Value |
|---|---|
| Estimated 1RM (Epley) | 116.7 |
| Brzycki | 112.5 |
Example 2
Inputs: Weight lifted = 60; Repetitions = 10.
| Result | Value |
|---|---|
| Estimated 1RM (Epley) | 80 |
| Brzycki | 80 |
The first line is the headline result (estimated 1RM (Epley)). Below it the one Rep Max Calculator lists brzycki, which describe the same case from other angles. IEEE-754 double precision; shown to 1 decimal place unless stated.
Why two answers
The formulas were fitted to different data. They agree closely at 2 to 5 reps and drift apart at higher reps; Brzycki cannot be used at 37 or more reps. Estimates become less reliable above about 10 reps.
Using the number
Percentages of 1RM guide training loads: roughly 85% for sets of 5 and 75% for sets of 10. Always warm up, use a spotter for heavy sets and do not attempt a true max without supervision. The estimate varies by exercise and by person.
How the result changes with weight lifted
Holding every other input at the first worked example, this table changes only weight lifted. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Weight lifted | Estimated 1RM (Epley) | Brzycki |
|---|---|---|
| 50 | 58.3 | 56.3 |
| 100 | 116.7 | 112.5 |
| 200 | 233.3 | 225 |
| 400 | 466.7 | 450 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Repetitions: entering "0" shows "Repetitions must be at least 1." beside that field and no result.
Choosing between the One Rep Max Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Training Load Calculator](/health/training-load-calculator/) | session RPE and duration of each session | Total training load |
| [Workout Volume Calculator](/health/workout-volume-calculator/) | sets per exercise, reps per set and weight per rep | Total volume |
| [Pace Calculator](/fitness/pace-calculator/) | distance and distance unit | Pace per km |
| [Lean Body Mass Calculator](/fitness/lean-body-mass-calculator/) | units, sex and weight | Lean body mass |
| [Rise Over Run Calculator](/fitness/rise-over-run-calculator/) | rise and run | Slope (rise ÷ run) |
Background: fitness estimates
Fitness formulas are estimates whose accuracy depends on the input. One-rep-max formulas such as Epley and Brzycki give different answers, and predictions from hard sets of a few repetitions are better than from sets of ten or more. Age-based maximum heart rate formulas can be off by 10 to 30 beats a minute for an individual; Tanaka's 208 − 0.7 × age is generally preferred to 220 − age but is still an estimate.
Pace models built from a race result assume a maximal effort and work best for distances from about 5 km to the marathon. Use the output as a guide, not a prescription.
Assumptions and limitations
- 1 rep returns the lifted weight under Epley × 1.033; Brzycki returns the weight
- Not a diagnosis
Estimates from formulas describe averages. They are not a training or medical prescription; check with a qualified professional before changing your exercise or diet.
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for repetitions to confirm this.
Frequently asked questions
Is the estimate exact?
No, treat it as a guide of a few percent.
Which formula is better?
Neither; use the same one to track progress.
Does it work for any lift?
It is best for compound lifts like squat, bench press and deadlift.
What does the One Rep Max Calculator calculate?
Estimate your one-repetition maximum from a heavier set. It returns Estimated 1RM (Epley) and Brzycki.
What formula does the One Rep Max Calculator use?
Epley: 1RM = w × (1 + reps ÷ 30); Brzycki: 1RM = w × 36 ÷ (37 − reps). Both formulas are least accurate above about 10 repetitions.
What do I need to enter in the one Rep Max Calculator?
You enter Weight lifted and Repetitions.
How is the result rounded or limited?
IEEE-754 double precision; shown to 1 decimal place unless stated. 1 rep returns the lifted weight under Epley × 1.033; Brzycki returns the weight.
What are the limits of this calculator?
1 rep returns the lifted weight under Epley × 1.033; Brzycki returns the weight. Not a diagnosis.
What is an example of a one Rep Max result?
With weight lifted 100 and repetitions 5, the estimated 1RM (Epley) is 116.7.
Where does the method come from?
The method follows: Epley B, Poundage Chart, Boyd Epley Workout (1985); Brzycki M, J Phys Educ Recreat Dance 1993;64:88–90.
Can I rely on this calculator for a decision?
Estimates from formulas describe averages. They are not a training or medical prescription; check with a qualified professional before changing your exercise or diet. For this calculator in particular: 1 rep returns the lifted weight under Epley × 1.033; Brzycki returns the weight.
Related calculators
- Training Load Calculator — Session load from perceived exertion and duration.
- Workout Volume Calculator — Total lifted volume from sets, reps and weight.
- Pace Calculator — Pace and speed from a distance and a time.
- Lean Body Mass Calculator — Estimate lean body mass with the Boer formula.
- Rise Over Run Calculator — Slope, grade and angle from rise and run.
- Winning Percentage Calculator — Winning percentage from wins, losses and ties.
- VO2 Max Estimate Calculator — Estimate VO2 max from a 12-minute run or from heart rates.
Sources
- Epley B, Poundage Chart, Boyd Epley Workout (1985)
- Brzycki M, J Phys Educ Recreat Dance 1993;64:88–90
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.