One rep max calculator: Epley and Brzycki, and where they disagree

Predicted one-rep max from 100 kg for 5 repsworked example

114.6 kg

Epley 1985: 116.67 kg
Brzycki 1993: 112.5 kg
How far apart the equations are: 4.17 kg3.6% of the midpoint
Published validation covers this rep count: yes, 2 to 10 reps

The headline is the midpoint of the two published equations, and the range beneath it is their own disagreement widened by the 3% mean error LeSuer and colleagues measured in 1997. LeSuer and colleagues tested these equations on the bench press, squat and deadlift in 1997 and found mean prediction error within about 3% between 2 and 10 reps. That is the range this estimate sits inside.

Realistic range

109.1 kg to 120.2 kg

The 3% figure is a mean across a study population on three barbell lifts; your own error on an unfamiliar movement, or on a set that stopped short of true failure, can be larger. Above 10 reps the validation simply does not reach, which is why the tool widens its language rather than quoting a number it does not have.

Weight lifted (kg)The prediction is a ratio, so the answer comes back in whatever unit you type in.Reps completedBetween 2 and 10 is where the published validation sits, and the set needs to have been genuinely close to failure.

Training percentages derived from the two equations, against a 114.6 kg max
Reps	Epley %	Epley kg	Brzycki %	Brzycki kg
1	96.8%	110.9	100%	114.6
2	93.8%	107.5	97.2%	111.4
3	90.9%	104.2	94.4%	108.2
4	88.2%	101.1	91.7%	105.1
5	85.7%	98.2	88.9%	101.9
6	83.3%	95.5	86.1%	98.7
7	81.1%	92.9	83.3%	95.5
8	78.9%	90.4	80.6%	92.4
9	76.9%	88.1	77.8%	89.2
10	75%	86	75%	86
11	73.2%	83.9	72.2%	82.7
12	71.4%	81.8	69.4%	79.5

Every row here is the two published equations inverted, not a chart copied off a wall. Read down the columns and you can see them cross: Epley sits above Brzycki up to nine reps, they are identical at ten, and Brzycki is higher after that.

A warm-up ladder to 100 kg, rounded to 2.5 kg steps
% of working weight	Reps	Weight	Loadable
40%	8	40 kg	40 kg
55%	5	55 kg	55 kg
70%	3	70 kg	70 kg
85%	2	85 kg	85 kg
95%	1	95 kg	95 kg

These percentages are a field convention, not a finding: no study prescribes 40/55/70/85/95. What the table is genuinely for is the arithmetic, rounded to plates you can actually put on a bar. The only part every strength text agrees on is that reps come down as the load goes up.

A one rep max calculator predicts the heaviest single you could lift from a set you actually completed. It runs Epley and Brzycki together, shows where they agree and where they diverge, gives the percentage table for every rep count, and widens the stated uncertainty above ten reps where the published validation stops.

One-rep max (Epley)convention — 1RM = weight x (1 + reps / 30). Verified 2026-07-30 against Epley 1985 (Boyd Epley Workout); accuracy reviewed in the JEPonline analysis of 1RM prediction equations (The original source is a 1985 coaching chart, not a journal paper - there is no published derivation, only the equation and decades of independent testing of it. LeSuer and colleagues found mean prediction error within about 3% between 2 and 10 reps. Above 10 reps no published accuracy figure covers it, and Epley and Brzycki pull apart quickly: at 15 reps they differ by roughly 9% of the midpoint.)
One-rep max (Brzycki) — 1RM = weight x 36 / (37 - reps), equivalently weight / (1.0278 - 0.0278 x reps). Verified 2026-07-30 against Brzycki, Journal of Physical Education, Recreation & Dance 1993 (Validated by LeSuer and colleagues in 1997 to within about 3% mean error at 2-10 reps. The equation has a hard mathematical limit: the denominator reaches zero at 37 reps, so the predicted max climbs towards infinity as rep counts get high, and it should not be read at all above roughly 12-15 reps. src/lib/health/strength.ts returns no value rather than a number once reps reach 37.)
One-rep-max prediction accuracy — mean prediction error within about 3% at 2-10 repetitions; no published figure above 10. Verified 2026-07-30 against LeSuer et al., Journal of Strength and Conditioning Research 1997 (The 3% figure is a mean across a study population on three barbell lifts; your own error on an unfamiliar movement, or on a set that stopped short of true failure, can be larger. Above 10 reps the validation simply does not reach, which is why the tool widens its language rather than quoting a number it does not have.)
Warm-up loading ladderconvention — 40% x 8, 55% x 5, 70% x 3, 85% x 2, 95% x 1 of the working weight. Verified 2026-07-30 against Derived from the Brzycki and Epley rep-to-percentage relationships; the specific percentages are a field convention (No study prescribes these particular percentages, and the site says so on the page. What the ladder is genuinely good for is arithmetic: five percentages of your working weight, rounded to a load you can actually build on a bar with the plates most gyms stock. The only part of the pattern every strength text agrees on is that reps descend as load climbs.)

Everything you type here is computed in your browser. Nothing you enter is stored on a server, sent anywhere, or shared — there is no account and no health data to leak.

Frequently asked questions

How do you calculate a one rep max?

Epley 1985 multiplies the weight by one plus your reps divided by 30. Brzycki 1993 multiplies it by 36 divided by 37 minus your reps. At 100 kilograms for 5 reps that is 116.67 and 112.5 kilograms, and this tool shows both instead of averaging them into one number.

Which one rep max formula is more accurate?

LeSuer and colleagues tested them on bench press, squat and deadlift in 1997 and found mean prediction error within about 3 percent between 2 and 10 reps, with no meaningful winner. Above 10 reps no published figure covers either of them, which is where this tool widens its language.

Why do Epley and Brzycki agree at exactly ten reps?

Because the arithmetic makes them identical there: one plus ten over 30 is 1.3333, and 36 over 27 is also 1.3333. Below ten reps Epley reads higher; above ten Brzycki does. That crossover is also almost exactly where the published validation runs out.

Why does Epley not return my weight at one rep?

It cannot. Weight times one plus one over 30 is 3.3 percent above the weight you just lifted once, which is arithmetically wrong, since a single already is your one rep max. Brzycki returns it exactly, because 36 over 36 is one. The tool says so on the result rather than smoothing it over.

How many reps should I use for the estimate?

Between 2 and 10 is where the published validation sits, and the set needs to have been genuinely close to failure. A set of 15 with three reps left in reserve produces a confident-looking number built on two guesses stacked on each other.

What percentage of my max should I train at?

That is a programming question rather than an arithmetic one, so this tool gives you the table and not a plan. It derives the percentage for each rep count from the two published equations themselves, so every row is arithmetic you can check.

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The next number

No body metric means much on its own. Here is what this one feeds into.

Protein calculatorThe number that most often limits what a lifting programme actually returns.Calories burned calculatorWhat a resistance session costs in energy terms, from the Compendium MET row for weight training.

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Every formula on this page is listed with its source on the methodology page, and changes to any reference value are logged in the data changelog. Canonical URL: https://myhealthmywellness.com/one-rep-max-calculator