One Rep Max Calculator
Your one-rep max (1RM) is the most weight you can lift for a single repetition of an exercise. Testing a true 1RM is risky and requires a spotter, so lifters usually estimate it from a lighter weight done for several reps. This calculator shows two well-known estimates — Epley and Brzycki — from the weight and reps you enter. Epley is highlighted as the most commonly used, and Brzycki is shown alongside it. Both are estimates that work best at lower rep counts (under about 10); they grow less accurate as reps rise, so treat the result as a training guide rather than a guaranteed number.
Calculate
Default result: 116.7
One Rep Max Calculator · Result
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Epley 1RM (most common)
100 × 5
- Brzycki 1RM
- 112.5
This calculator provides general estimates for educational purposes only and is not medical advice. Results are based on population formulas and may not reflect your individual circumstances. Consult a qualified healthcare professional before making changes to your diet, exercise, or health routine.
Reviewed by the calculators.dev team · Last updated 2026-06-23
Formula reviewed against Epley B. Poundage chart. Boyd Epley Workout, 1985 (Epley 1RM formula)
How to calculate
Enter the weight you lifted and the number of clean reps you completed (1 to 36). The calculator applies both formulas: Epley is weight × (1 + reps ÷ 30), and Brzycki is weight × 36 ÷ (37 − reps). For 100 × 5 that is 116.7 and 112.5. Use a set you finished with good form — ideally in the 3–8 rep range, where the estimates are most reliable. Programs often prescribe loads as a percentage of 1RM, so the estimate helps you pick working weights without maxing out.
Epley: 1RM = weight × (1 + reps ÷ 30). Brzycki: 1RM = weight × 36 ÷ (37 − reps). Variables: weight is the load lifted and reps is the repetitions completed. The result is in the same unit you lifted. Brzycki is undefined at 37 reps (the denominator hits zero), so very high-rep sets are unreliable for both formulas; estimates are most accurate under roughly 10 reps.
Example calculation
Lifting 100 (kg or lb) for 5 reps gives an Epley 1RM of 100 × (1 + 5 ÷ 30) = 116.7 and a Brzycki 1RM of 100 × 36 ÷ (37 − 5) = 112.5. The two formulas agree closely at low reps and drift apart as the rep count rises, so they bracket your likely max.
- epley
- 116.7
- brzycki
- 112.5
Assumptions
- Both formulas assume the reps were performed to near-failure with good technique; a submaximal set understates the true 1RM.
- Accuracy is best at low rep counts (roughly 1–10) and degrades as reps climb, which is why two formulas are shown to bracket the estimate.
- 1RM varies by exercise, fatigue, and the day; the number is a guide for programming, not a fixed personal record.
Common mistakes
- Estimating from a very high-rep set. Above about 10 reps the formulas diverge and overstate the max — use a heavier set with fewer reps.
- Treating the estimate as a target to actually attempt. A true 1RM test needs a spotter and proper warm-up; do not chase the predicted number unsafely.
- Counting sloppy or assisted reps. Only clean, full-range reps to near-failure give a meaningful estimate.
Frequently asked questions
How do I calculate my one-rep max?
Take a weight you lifted for a few reps and apply a formula. The Epley estimate is weight × (1 + reps ÷ 30); for 100 × 5 that is about 116.7. This calculator also shows the Brzycki estimate for comparison.
Which 1RM formula is most accurate?
Epley and Brzycki are both widely used and agree closely at low reps. Neither is definitively best — they drift apart at higher reps, so the pair gives a useful range rather than one exact figure.
How many reps should I use to estimate 1RM?
A set in the 3–8 rep range taken close to failure gives the most reliable estimate. Above about 10 reps the formulas become inaccurate and tend to overestimate.
Should I actually test my one-rep max?
Estimating is safer and usually enough for programming. A true 1RM test carries injury risk and should only be done with a proper warm-up, good form, and a spotter.