Estimates only. Not guaranteed results, not medical advice.
One Rep Max Calculator
Estimate your one rep max from a set you have actually lifted. Six published formulas, the honest range between them, training percentages, plate loading and warm-up sets — free, instant, no signup.
1RM calculator
Plate loader
Warm-up sets
Prefilled with the set you entered. Change the top set to plan a different session.
Save or share this result
A share link stores your inputs in the page address (for example ?w=225&r=5&u=lb). Nothing is sent to us; anyone with the link sees the same calculation.
What is a one rep max?
A one rep max (1RM) is the heaviest weight you can lift for a single, complete repetition with good technique. An estimated 1RM predicts that number from a lighter set you did for several reps, so you do not have to attempt a true max.
Coaches use the 1RM to set training loads: “5 sets of 5 at 80%” means 80% of your one rep max. Estimating it from a set of 3–6 reps is safer and less fatiguing than testing it, which is why most lifters use a calculator between occasional tested maxes.
How the calculator works
- Enter a set you actually lifted — the weight, how many clean reps you completed, and your unit.
- Six published formulas run on it — Epley, Brzycki, Lombardi, Mayhew, O’Conner and Wathan. Every equation is shown below; nothing is hidden.
- You get the honest range — the Average Estimate (the plain mean of the six), the lowest and highest formula, how far apart they are, and a confidence note tied to your rep count.
- Training tools use the result — a percentage table, 2RM–10RM estimates, a plate loader and a warm-up generator, all rounded down to weights you can actually load.
If you lifted a true single (1 rep), there is nothing to estimate: every formula returns the weight you entered. See the methodology for every rounding rule and the automated checks behind the numbers.
The six 1RM formulas, side by side
Each formula estimates 1RM from a weight w lifted for r reps. They were built from different groups of lifters and different assumptions, so they give different answers for the same set.
| Formula | Equation | Origin | How it behaves |
|---|---|---|---|
| Epley | 1RM = w × (1 + r ÷ 30) | Boyd Epley’s 1985 poundage chart — a coaching tool rather than a peer-reviewed study. | Linear: adds 3.33% per rep. Sits in the middle of the six from 2 to 10 reps. |
| Brzycki | 1RM = w × 36 ÷ (37 − r) | Matt Brzycki, Journal of Physical Education, Recreation & Dance (1993). | Lowest of the six at 2–5 reps (tied with O’Conner at 5), identical to Epley at 10 reps, and highest at 11–12 reps as its curve steepens. Undefined at 37 reps. |
| Lombardi | 1RM = w × r^0.10 | V. P. Lombardi’s textbook Beginning Weight Training (1989). | Power curve that flattens as reps rise: mid-pack at low reps, lowest of the six at 11–12 reps. |
| Mayhew | 1RM = 100w ÷ (52.2 + 41.9e^(−0.055r)) | Mayhew and colleagues (1992), fitted to bench-press data from college men and women. | Exponential. Highest of the six at 1–6 reps: it is not anchored to a single (it gives about 109% of the weight for 1 rep), so it reads high on very heavy sets. |
| O'Conner | 1RM = w × (1 + 0.025 × r) | O’Conner, Simmons and O’Shea’s textbook Weight Training Today (1989). | Linear: adds 2.5% per rep. Lowest of the six at 6–10 reps. |
| Wathan | 1RM = 100w ÷ (48.8 + 53.8e^(−0.075r)) | Dan Wathen’s chapter in the NSCA textbook Essentials of Strength Training and Conditioning (1994); often spelled “Wathan”. | Exponential. Within about 1% of Epley at 3–8 reps and highest of the six at 7–10 reps. |
w = weight lifted, r = reps completed, e ≈ 2.718.
For a rep-by-rep comparison and when each formula tends to read high or low, see the1RM formula guide. Lander’s formula, used on some other calculators, is deliberately not included until its equation is verified against its original published source.
How to read your result
- Average Estimate: a convenient single number for planning — the middle of the six formulas, not a promise.
- Range and spread: how much the formulas disagree on your set. On a 5-rep set they differ by about 6%; at 12 reps, by more than 12%.
- Programming from it: many training programs start from a deliberately conservative “training max” below the estimate (often around 90%), so early sessions are achievable.
- Re-test with fresh sets: re-estimate every few weeks from a new heavy set rather than chasing the number by testing often.
Accuracy and limitations
- Estimates are not tested maxes. They predict what you could lift once; fatigue, sleep, stress and the day itself are invisible to every formula.
- Accuracy depends on the lift. In a study of seven equations on the bench press, squat and deadlift, all of them significantly underestimated the deadlift (LeSuer et al., 1997).
- Fewer reps, better estimates. Predictions from 5-rep maxes were more accurate than from 10- or 20-rep maxes (Reynolds et al., 2006). Above 10 reps the formulas diverge sharply; above 12 this calculator shows no number.
- Only count clean reps. Bounced, half-range or assisted reps inflate every estimate.
- Beginners: estimate from a submaximal set of 5–8 reps rather than attempting a true max. See how to test your 1RM safely.
All calculators
- Bench Press Calculator
Estimate your bench max, with what counts as a clean rep.
- Squat Calculator
Estimate your squat max — and why depth changes the number.
- Deadlift Calculator
Estimate your deadlift max, and why formulas may read low.
- Overhead Press Calculator
Estimate a strict press max and plan small, loadable jumps.
- Barbell Row Calculator
Estimate a row max for programming — with honest caveats.
- 1RM Percentage Calculator
Turn a known 1RM into working weights, e.g. 80% for sets of five.
- Plate Calculator
See which plates to load per side — never over your target.
- Warm-up Calculator
Build a warm-up ramp to your top set, with loadable weights.
- RPE Calculator
Estimate your 1RM from a set rated by RPE, and plan weights by reps in reserve.
- DOTS Calculator
Score a powerlifting total against bodyweight with the DOTS formula.
Frequently asked questions
What is a one rep max?
A one rep max (1RM) is the heaviest weight you can lift for one complete repetition of an exercise with good technique. Lifters and coaches use it to measure maximal strength and to set training weights as percentages of it.
How do I calculate my 1RM?
Take a set you lifted with good form, then apply a 1RM formula. With Epley, 1RM = weight × (1 + reps ÷ 30), so 225 lb for 5 reps estimates about 262.5 lb. This calculator runs six published formulas at once and shows each result, the Average Estimate and the range between them.
Which 1RM formula is most accurate?
No single formula is most accurate for everyone. Research has found that accuracy depends on the lift, the lifter and the rep count — in one study comparing seven equations, every one underestimated the deadlift. That is why StrengthCalc shows all six results and the spread instead of a single number.
How many reps should I use for a 1RM estimate?
Use a set of about 3 to 6 clean reps taken close to failure. Heavier sets need less extrapolation, and a 2006 study found 5-rep-max tests predicted 1RM more accurately than 10- or 20-rep tests. This calculator accepts 1 to 12 reps and shows no number above 12.
Is a calculated 1RM accurate?
It is an estimate, not a measurement. Estimates from heavy, near-failure sets are usually a useful guide for programming, but your true max can be higher or lower depending on technique, fatigue, experience and the exercise. Only a tested single tells you your actual 1RM on that day.
What is the difference between a 1RM and an estimated 1RM?
A 1RM is the weight you actually lift once. An estimated 1RM (often written e1RM) is a prediction calculated from a heavier-than-one-rep set, such as 5 reps. Estimating avoids the fatigue and injury risk of a true max attempt, at the cost of some accuracy.
How do I calculate 80% of my 1RM?
Multiply your 1RM by 0.80. For a 300 lb max, 80% is 240 lb; for a 140 kg max, it is 112 kg. The percentage table in your results, and the 1RM Percentage Calculator, do this for every common percentage and round down to a weight you can load.
What is the Average Estimate?
The Average Estimate is the plain arithmetic mean of the six formula results. It summarises where the formulas cluster; it is not a scientifically validated consensus and is not claimed to be more accurate than any single formula.
Should beginners test their 1RM?
Usually not. Beginners gain more from practising technique, and can estimate their max from a submaximal set of 5–8 reps instead. A true max attempt needs consistent technique, proper equipment and a spotter or safety arms.
Should I use kg or lb?
Use whichever unit you train in. The math is identical; switching units converts what you typed and every result is also shown in the other unit (1 kg = 2.20462 lb).
Sources
- Epley, B. (1985). Poundage Chart. Boyd Epley Workout. Lincoln, NE: Body Enterprises. (A coaching chart, not a peer-reviewed study.)
- Brzycki, M. (1993). Strength testing — predicting a one-rep max from reps-to-fatigue. Journal of Physical Education, Recreation & Dance, 64(1), 88–90. Link (opens in a new tab)
- Lombardi, V. P. (1989). Beginning Weight Training: The Safe and Effective Way. Dubuque, IA: Wm. C. Brown.
- Mayhew, J. L., Ball, T. E., Arnold, M. D., & Bowen, J. C. (1992). Relative muscular endurance performance as a predictor of bench press strength in college men and women. Journal of Applied Sport Science Research, 6(4), 200–206.
- O’Conner, B., Simmons, J., & O’Shea, P. (1989). Weight Training Today. St. Paul, MN: West Publishing.
- Wathen, D. (1994). Load assignment. In T. R. Baechle (Ed.), Essentials of Strength Training and Conditioning (pp. 435–446). Champaign, IL: Human Kinetics.
- LeSuer, D. A., McCormick, J. H., Mayhew, J. L., Wasserstein, R. L., & Arnold, M. D. (1997). The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift. Journal of Strength and Conditioning Research, 11(4), 211–213.
- Reynolds, J. M., Gordon, T. J., & Robergs, R. A. (2006). Prediction of one repetition maximum strength from multiple repetition maximum testing and anthropometry. Journal of Strength and Conditioning Research, 20(3), 584–592. Link (opens in a new tab)