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Orpheus

One Rep Max Calculator

Four formulas side by side, and the working weights they imply.

Inputs
kg or lb
reps

Clean reps to near failure. Above about twelve, every formula stops being reliable.

Estimated one rep max
115kg or lb
ReliableGoodLooseUnreliable

Good

95% — about 2 reps
109
93% — about 3 reps
106.5
90% — about 4 reps
103.5
87% — about 5 reps
100
85% — about 6 reps
97.5
80% — about 8 reps
92
75% — about 10 reps
86
70% — about 12 reps
80.5
Spread across the four formulas
5
Epley: w x (1 + r ÷ 30) · Brzycki: w x 36 ÷ (37 − r)

The scale shows how much to trust the estimate: it is derived from your rep count, and every formula degrades as reps climb. The unit is whatever you entered — the maths is the same in kilograms or pounds.

Every tool runs entirely in your browser. Your files are never uploaded to a server.

A one rep max is estimated from a heavier set by fitting a curve through the relationship between load and reps. Estimates are dependable up to about five reps and drift apart above ten, where the formulas disagree by several percent.

How to use One Rep Max Calculator

  1. Use a set taken close to failure. Enter the weight and the number of clean reps. A set with reps left in reserve underestimates.
  2. Keep the rep count low. Five or fewer is where the formulas agree. Above ten they diverge and the estimate is worth little.
  3. Read the percentage table. Beneath the estimate are the loads for common rep ranges, which is what a programme is usually written against.

About one rep max

Every one rep max formula is a curve fit rather than a law. Researchers measured how many reps lifters completed at various fractions of a known maximum, then fitted an equation to the pattern. Epley, published in 1985, is linear in reps and reads slightly high at the top end. Brzycki, from 1993, divides by a term that shrinks as reps climb and reads lower; it also breaks down entirely above around thirty-six reps, where its denominator approaches zero. Lombardi uses a power curve and O'Conner a gentler linear one. That they disagree is the useful information, and the spread shown here is a direct measure of how much confidence the estimate deserves. What none of them can capture is the individual. Two lifters with the same three-rep max can have genuinely different single-rep maxima, because the relationship between maximal strength and rep endurance depends on muscle fibre composition, training history and how comfortable someone is under a heavy bar. Lifters who train predominantly in low rep ranges tend to outperform the estimate; those who train in higher ranges tend to fall short of it. Use the number to select working weights, review it every few weeks against what actually moved, and treat a percentage table as a starting point rather than a prescription.

Frequently asked questions

Which one rep max formula is most accurate?
None is reliably best. Brzycki tends to read lower at higher reps and Epley higher, and Lombardi is more forgiving still. Taking the average of several is more honest than picking one, which is why it is the default here.
How many reps can I use?
Up to about five gives a dependable estimate. Between six and ten it loosens. Above twelve the formulas are extrapolating well past the data they were fitted to, and muscular endurance starts to matter more than maximal strength.
Should I actually test my one rep max?
Rarely, and not without experience and a spotter. A true maximal attempt carries real injury risk and needs recovery. Estimating from a set of three to five is safer and accurate enough for programming.
Does this work for every lift?
Best for compound barbell lifts — squat, bench, deadlift, press — which is what the formulas were fitted on. Isolation movements and machines produce noisier estimates because form and leverage vary more between reps.
Why does the estimate use no units?
Because the maths is a ratio, so it works identically in kilograms and pounds. Whatever unit you enter is the unit that comes out.

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