Training tools
One-Rep Max Calculator
Estimate your 1RM from any heavy set — including sets you stopped short of failure — compare the main prediction equations and turn the result into working weights. The method and its limits are explained below, with sources.
Calculator
Unit
Estimated one-rep max
265 lb
| Brzycki | 261.3 lb |
|---|---|
| Epley | 270 lb |
| Lombardi | 269.2 lb |
Unrounded. The spread between equations is a reminder that each is an estimate.
Estimated rep maxes and working weights
| Reps | Load | % of 1RM | RPE |
|---|---|---|---|
| 1 | 265 lb | 100% | 10 |
| 2 | 255 lb | 95% | 10 |
| 3 | 245 lb | 93% | 10 |
| 4 | 240 lb | 90% | 10 |
| 5 | 230 lb | 87% | 10 |
| 6 | 225 lb | 85% | 10 |
| 8 | 210 lb | 80% | 10 |
| 10 | 200 lb | 75% | 10 |
With 0 in reserve, each row is an estimated rep max (e.g. 5 reps = your estimated 5RM).
What a one-rep max is
A one-rep max (1RM) is the heaviest load you can lift once, through a full range with acceptable technique. It is the standard measure of maximal strength and the reference for percentage-based programmes.
Unless you actually perform a maximal single, any 1RM figure is an estimate. Testing directly is the most accurate method, but it is fatiguing, takes skill to do well and should not be attempted alone without safeties. A heavy set of several reps contains most of the same information, which is what this calculator uses.
How the estimate works
The calculator counts how far the set was from failure — the reps you did plus the reps you had left in reserve. RPE and reps in reserve describe the same thing: RPE 10 is a set with no reps left, RPE 9 one rep left, RPE 8 two [1] [2].
It then applies three long-standing equations. Brzycki’s was published in 1993 [3]; Epley’s and Lombardi’s come from a 1985 coaching manual and a 1989 textbook rather than journals. The headline figure averages Brzycki and Epley, because a validation study in 220 men suggested that averaging two equations may reduce the error of any single one [4]. Lombardi is shown for comparison: it gives noticeably lower estimates than the other two as the rep count rises.
- Brzycki: 1RM = load × 36 / (37 − reps)
- Epley: 1RM = load × (1 + reps / 30)
- Lombardi: 1RM = load × reps^0.10
How accurate is it?
Rep-based equations correlate strongly with tested maxes, but individual predictions can be off by several kilograms. In the 1995 bench press study, accuracy was best for sets of 10 reps or fewer to failure — where Brzycki’s equation was the most accurate of those tested — and every equation drifted, some high and some low, beyond 10 reps [4]. A later study of chest and leg press found that a 5RM gave the most accurate prediction and that no more than 10 repetitions should be used [5]. That is why the calculator stops at 12 reps from failure and works best with sets of 3–8.
No equation is the most accurate for everyone: the best one differs between studies, exercises and people. The second source of error is your own estimate of reps in reserve, which is better on heavy sets and later sets than on light, early ones [6].
Limitations
Treat the number as a planning figure for setting loads, not a substitute for a tested max in competition.
- Validation studies have mostly used the bench press, squat and machine presses. The number of reps possible at a given percentage differs between exercises — more in the squat than the bench press or curl at the same %1RM [7].
- Endurance-trained people can do more reps at moderate percentages than strength-trained people [8], so the same set tends to overestimate an endurance athlete’s max.
- A set that ended because of grip, breathing or technique — not the target muscles — underestimates your max.
Using it to set training loads
For strength, most main-lift work sits at roughly 1–6 reps with 1–3 reps in reserve; muscle growth responds to a much wider range of loads when sets are taken close to failure [9]. Our guide to how heavy to lift explains the trade-offs, the RPE calculator builds a full effort-based chart, and the percentage calculator gives loads for any %1RM.
Re-estimate every few weeks from a recent heavy set rather than retesting a true max. If a prescribed load feels clearly easier or harder than intended on the day, adjust it — the effort target matters more than the percentage.
Frequently asked questions
Which 1RM formula is most accurate?
None is accurate for everyone. In a bench press validation study, Brzycki’s equation was the most accurate for sets of 10 reps or fewer to failure, and averaging two equations was suggested to reduce error [4]. That is the approach this calculator takes, with Lombardi shown for comparison.
How many reps should I use to estimate my max?
Sets of about 3–8 reps from failure give the most dependable estimates; a 5RM predicted best in one study, and estimates become less accurate beyond 10 reps [5] [4].
Do I need to go to failure for an accurate estimate?
No. Enter the reps you did and how many you had left. Your estimate of reps in reserve is more accurate on heavy sets than on light ones [6], so use a heavy set.
Sources
- [1]Zourdos MC, Klemp A, Dolan C, et al. Novel Resistance Training-Specific Rating of Perceived Exertion Scale Measuring Repetitions in Reserve. Journal of Strength and Conditioning Research. 2016;30(1):267–275. Source
- [2]Helms ER, Cronin J, Storey A, Zourdos MC. Application of the repetitions in reserve-based rating of perceived exertion scale for resistance training. Strength and Conditioning Journal. 2016;38(4):42–49. Source
- [3]Brzycki M. Strength testing—predicting a one-rep max from reps-to-fatigue. Journal of Physical Education, Recreation & Dance. 1993;64(1):88–90. Source
- [4]Mayhew JL, Prinster JL, Ware JS, Zimmer DL, Arabas JR, Bemben MG. Muscular endurance repetitions to predict bench press strength in men of different training levels. Journal of Sports Medicine and Physical Fitness. 1995;35(2):108–113. Source
- [5]Reynolds JM, Gordon TJ, Robergs RA. Prediction of one repetition maximum strength from multiple repetition maximum testing and anthropometry. Journal of Strength and Conditioning Research. 2006;20(3):584–592. Source
- [6]Hickmott LM, Butcher SJ, Chilibeck PD. A comparison of subjective estimations and objective velocities at quantifying proximity to failure for the bench press in resistance-trained men and women. Journal of Strength and Conditioning Research. 2024;38(7):1206–1212. Source
- [7]Shimano T, Kraemer WJ, Spiering BA, et al. Relationship between the number of repetitions and selected percentages of one repetition maximum in free weight exercises in trained and untrained men. Journal of Strength and Conditioning Research. 2006;20(4):819–823. Source
- [8]Richens B, Cleather DJ. The relationship between the number of repetitions performed at given intensities is different in endurance and strength trained athletes. Biology of Sport. 2014;31(2):157–161. Source
- [9]Schoenfeld BJ, Grgic J, Ogborn D, Krieger JW. Strength and hypertrophy adaptations between low- vs. high-load resistance training: a systematic review and meta-analysis. Journal of Strength and Conditioning Research. 2017;31(12):3508–3523. Source
Keep going
Related guides
Strength guides that use these numbers, and the equipment for training heavy safely at home.
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How to Get Stronger: An Evidence-Based Guide to Strength Training
The principles that drive strength gains — heavy loads, specific practice, frequency, volume and periodisation — and how to build them into a programme.
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How Many Reps for Strength? Choosing Your Loads
How load and rep range affect strength and muscle growth, what percentage of your max to use, and how to combine heavy and moderate work.
Training Fundamentals
Progressive Overload: How to Keep Making Progress
What progressive overload really means, why adding reps works as well as adding weight, and a simple double-progression system you can use on every exercise.
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