One-rep max (1RM) calculator

Calculator

What a one-rep max is, and why estimate it

One repetition maximum is the standard laboratory and gym measure of dynamic maximal strength: the greatest load you can move through a full range of motion once, with technique that would pass in a competition or a coach's eye. It is the number sports science uses to compare athletes, the number powerlifting is scored on, and the number that gives percentage-based programming something to be a percentage of.

Testing it directly means working up through progressively heavier singles until you fail, which takes half an hour or more, leaves you too tired to train usefully afterwards, and carries real injury risk on lifts where failure means the bar landing on you. Repeat that every few weeks for three or four lifts and a meaningful share of your training year has gone into testing rather than training.

Prediction equations exist to avoid that trade-off. Each one was fitted by having a group of people perform a true 1RM and then a set to failure at a lighter weight, and finding the curve that best maps repetitions onto a fraction of maximum. Because they were fitted on different people doing different lifts, they produce different curves, which is why this page shows all of them rather than pretending one is the answer.

How to take the test set so the estimate means something

Every equation assumes one thing about your set: that it ended within about one repetition of true failure. If you stopped with three left in the tank, the equation reads your set as harder than it was and gives you a number well below your real max. Getting the set right matters far more than which equation is used to convert it.

Warm up properly first: the estimate is fitted on warmed-up lifters, not on a first working set. Ramp in five or six steps to the test weight, keeping the reps low so you arrive fresh: something like ten with the empty bar, five at forty per cent, three at sixty, two at seventy-five, one at eighty-five, then the test set. Rest three to five minutes before it. Then pick a load you expect to manage for three to six reps and take it until the bar slows to a crawl.

Stop the set the moment technique breaks rather than the moment the bar stops moving. A squat where the knees cave in, a bench press where the hips leave the bench, a deadlift where the back rounds: those reps are not the reps the equations were fitted on, and counting them inflates the estimate while doing the thing most likely to hurt you.

• Aim for three to six repetitions: the error band is narrowest there and the set is still safe to take to near-failure.
• Have a spotter on bench press and squat, or set the safety pins at a height you can escape under.
• Use the same bar, the same shoes, the same depth and the same tempo each time you test, or you are measuring the change in conditions rather than the change in strength.
• Do the test early in a session, not after the work that would normally fatigue that lift.
• Count only the repetitions that met your own technical standard. The rep you argued with yourself about does not count.

Reading the spread between the seven equations

The seven estimates on your result are not seven guesses at the same thing that should be averaged out of politeness. They are seven different curves fitted to seven different samples, and the distance between the highest and lowest is a direct readout of how much the published literature disagrees about a set like yours. A small spread means your rep count sits in the region where the curves overlap and the estimate is dependable. A wide one means you are out on the part of the curve where the fits diverge.

At five repetitions the spread is typically five to six per cent of the mean: at a hundred kilograms lifted five times, roughly a six-kilogram gap between the most and least generous equation. At two or three repetitions it narrows to two or three per cent. At ten or twelve it opens out past ten per cent, which is the arithmetic behind the advice to keep test sets short.

The headline figure on this page is the mean of the seven, and that is a deliberate choice rather than a fudge. LeSuer and colleagues tested all seven against measured maxima in the bench press, squat and deadlift and found no single equation was best across all three lifts: Wathan and Mayhew came closest on the bench press, while others fitted the squat and deadlift better. With no clear winner, the centre of the spread is the defensible answer, and the spread itself is what you should quote alongside it.

Why the estimate gets worse as the reps go up

Maximal strength and muscular endurance are related but separate qualities, and the number of repetitions you can complete at a given percentage of your max depends heavily on which of the two you have trained. A powerlifter and a rower with identical one-rep maxima will not manage the same number of reps at seventy per cent; the rower will usually manage more, sometimes far more. Every prediction equation assumes a single fixed relationship between reps and percentage, so the further from a single repetition you test, the more of the person's own endurance profile leaks into the answer.

Richens and Cleather demonstrated this directly by comparing endurance-trained and strength-trained athletes at the same relative loads and finding significantly different repetition counts. The practical consequence is that a set of twelve tells you a great deal about how conditioned you are and rather less about what you could lift once. Lower-body lifts show the effect strongly: most people manage several more repetitions at a given percentage in the squat than in the bench press.

This calculator stops at twelve repetitions for that reason. Beyond it the equations produce numbers that look authoritative and are not, and the right answer is simply to test again with a heavier bar rather than to extrapolate from a set that was never about maximum strength.

Turning your max into training loads

Percentage-based programming is the main reason anyone wants this number. Once you have a working max, the load for each session follows from the block you are running: heavy strength work in the eighty-five to ninety-five per cent range, strength and size together around eighty, hypertrophy work between sixty-five and seventy-five, and technique or speed work below sixty. The table on this page gives the actual bar weight for each of those percentages, rounded to the nearest loadable pair of plates.

The repetition figures beside each percentage are the conventional strength-and-conditioning ranges rather than a published regression, and the American College of Sports Medicine's progression models position stand is explicit that the load–repetition relationship varies with training status, lift and individual. Treat them as a starting point. If the programme calls for five reps at eighty-five per cent and you make eight without slowing, your working max has moved and the number needs updating; if you stall at three, it has not.

Most coaches keep a training max slightly below the tested or estimated figure (commonly ninety to ninety-five per cent of it) precisely so the programmed percentages stay achievable on an ordinary day rather than only on a good one. Feeding a generous estimate straight into a percentage block is the most common way a programme quietly becomes too heavy by week three.

When a true max attempt is worth the risk

There are situations where an estimate will not do. If you are competing in powerlifting or weightlifting you need real singles, because opener and attempt selection on the platform depends on knowing what a maximal lift feels like and not just what it weighs. Athletes in testing batteries are often required to produce a measured 1RM to a protocol. And anyone who has trained for years without ever taking a genuine single is missing a skill: bracing, tightness and nerve under a maximal load are trainable and do not appear by themselves.

When you do test, the protocol matters. Warm up thoroughly, rest three to five minutes between attempts, increase in small steps near the top, and stop after three or four failed-or-successful maximal attempts. Accuracy degrades as fatigue accumulates. Use a competent spotter on the bench press and squat, or a rack with pins set where you can dump the bar safely. Grgic and colleagues' systematic review found 1RM testing to be highly reliable when it follows a standardised protocol in trained lifters, and rather less so in beginners, which is the main argument for estimating rather than testing early on.

For everyone else (most lifters, most of the time), a set of five taken close to failure gives you a number good to within a few per cent, costs one set of fatigue, and can be repeated every few weeks without a spotter or a taper. That is the trade this calculator exists to make.

What the number means next to everyone else's

One-rep maxima are usually compared as a multiple of body weight, because absolute load favours larger lifters so heavily that the raw kilograms tell you little on their own. The rough conventions in general strength training put a bench press at body weight, a squat at one and a half times, and a deadlift at twice body weight as solid intermediate benchmarks for men, with women's ratios typically lower on upper-body lifts and closer on lower-body ones. These are gym conventions rather than validated cut-offs, so treat them as orientation, not as a scale to be judged against.

Body composition explains much of the difference between people at the same body weight. Strength tracks fat-free mass far more closely than it tracks total mass, which is why comparing your lifts with someone else's is more informative once you know roughly what each of you is carrying. The fat-free mass index and lean body mass calculators here give you that context from measurements you already have.

The most useful comparison, though, is with yourself. Estimated the same way from the same lift with the same technical standard, this number tracks real strength change reliably even when its absolute accuracy is a few per cent out. Log the weight and reps rather than only the estimate, so that a future you can re-run the arithmetic if the method changes.

How it's calculated

Worked example: 100 kg lifted for 5 repetitions

1. Epley: 100 × (1 + 5 ÷ 30) = 100 × 1.1667 = 116.7 kg.
2. Brzycki: 100 × 36 ÷ (37 − 5) = 100 × 36 ÷ 32 = 112.5 kg.
3. Lombardi: 100 × 5^0.10 = 100 × 1.1746 = 117.5 kg.
4. O'Conner: 100 × (1 + 0.025 × 5) = 100 × 1.125 = 112.5 kg.
5. Lander: 100 × 100 ÷ (101.3 − 2.67123 × 5) = 10,000 ÷ 87.944 = 113.7 kg.
6. Mayhew: 10,000 ÷ (52.2 + 41.9 × e^(−0.275)) = 10,000 ÷ 84.026 = 119.0 kg.
7. Wathan: 10,000 ÷ (48.8 + 53.8 × e^(−0.375)) = 10,000 ÷ 85.776 = 116.6 kg.
8. Take the mean of the seven: 808.4 ÷ 7 = 115.5 kg, the headline estimate.
9. Read the spread: the estimates run from 112.5 kg to 119.0 kg, a gap of 6.5 kg or 5.6 per cent of the mean. The honest statement is 'about 115 kg, somewhere between 112 and 119'.
10. Convert to a training load: 85 per cent of 115.5 is 98.2 kg, which rounds to 97.5 kg on a bar loaded with 2.5 kg pairs, a sensible weight for sets of five.

Where this number is used in the real world

• Percentage-based programming, where every prescribed load in a strength block (5 × 5 at 80 per cent, singles at 90, back-off sets at 65) is a fraction of this number.
• Powerlifting meet preparation, where opener and second-attempt selection is conventionally set from a recent estimated or tested max and the third attempt is the stretch.
• Tracking strength change over a training cycle, since the same lift estimated the same way month to month shows the trend even when the absolute figure is a few per cent out.
• Sports testing batteries, where squat and bench 1RM relative to body weight is a standard entry in an athlete profile alongside sprint, jump and body composition measures.
• Rehabilitation and return-to-play progression, where a clinician prescribes loads as a percentage of a max estimated from a light, safe set rather than tested directly.
• Setting the load on gym machines and in group classes, where the stack number means nothing until it is expressed as a share of what you can move once.

Frequently asked questions

Keep going

A single number rarely tells the whole story. Alongside the one-rep max result, the FFMI calculator, the lean body mass calculator, the protein calculator and the TDEE calculator each add a different angle on the same measurements. For the reasoning behind the numbers, read BMI for athletes, Track without DEXA and TDEE explained.

Sources

1. Brzycki M. Strength testing: predicting a one-rep max from reps-to-fatigue. Journal of Physical Education, Recreation and Dance 1993;64(1):88–90. doi.org/10.1080/07303084.1993.10606684
2. Mayhew JL, Ball TE, Arnold MD, Bowen JC. Relative muscular endurance performance as a predictor of bench press strength in college men and women. Journal of Applied Sport Science Research 1992;6(4):200–6. doi.org/10.1519/00124278-199211000-00002
3. LeSuer DA, McCormick JH, Mayhew JL, Wasserstein RL, Arnold MD. The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift. Journal of Strength and Conditioning Research 1997;11(4):211–13. doi.org/10.1519/00124278-199711000-00001
4. 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):584–92. doi.org/10.1519/R-15304.1
5. Grgic J, Lazinica B, Schoenfeld BJ, Pedisic Z. Test-retest reliability of the one-repetition maximum (1RM) strength assessment: a systematic review. Sports Medicine – Open 2020;6:31. doi.org/10.1186/s40798-020-00260-z
6. American College of Sports Medicine. Position stand: progression models in resistance training for healthy adults. Medicine and Science in Sports and Exercise 2009;41(3):687–708. doi.org/10.1249/MSS.0b013e3181915670
7. 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):157–61. doi.org/10.5604/20831862.1099047