How accurate is a one rep max estimate?

Good within a few percent from a set of two to five. Above ten reps the formulas disagree with each other and with reality, because endurance and maximal strength diverge.

Should I test my actual max?

A true maximal attempt carries injury risk and needs technique that holds under load. Most training programmes work from estimates for exactly that reason.

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One Rep Max Calculator

One rep max estimated from a set. The formulas agree closely up to about five reps and diverge sharply beyond ten, so a set of three predicts far better than a set of fifteen.

Also called: 1rm calculator, max lift calculator.

Estimated one rep max

116.67

116.67 kg by the Epley formula, from 5 reps at 100 kg. The other formulas give Epley 116.7, Brzycki 112.5, Lombardi 117.5 kg. Working weights: 105 kg for 90%, 93.33 kg for 80% and 81.67 kg for 70%. A low rep set gives a reliable estimate, and the formulas agree closely here.

90 percent

105

80 percent

93.33

70 percent

81.67

Approximate reps at 80 percent

Other formulas

Epley 116.7, Brzycki 112.5, Lombardi 117.5 kg

Formula used

Epley

On accuracy

A low rep set gives a reliable estimate, and the formulas agree closely here.

How this is calculated

Method and background

This is what the calculation gives for the numbers you entered. It is an estimate, not advice, and it knows nothing about your situation beyond those numbers. Rules for United States change on a published schedule; the effective date is shown on every rule-based tool.

How this is calculated

Each formula fits a curve relating reps to a fraction of maximum. They agree within a couple of percent at low rep counts and separate substantially above ten, because the relationship between endurance and maximal strength varies far more between people at higher reps. A set of two to five gives a usable estimate; a set of fifteen tells you more about muscular endurance than about maximum strength. Showing all three makes the spread visible.

Epley, one of several regressions that agree closely at low reps and diverge above about ten

w: Weight lifted
r: Reps

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

five reps at 100 kg

Weight lifted: 100 kg
Repetitions completed: 5
Formula: Epley

Estimated one rep max116.67

100 x (1 + 5/30)

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one rep is the max itself

Weight lifted: 100 kg
Repetitions completed: 1
Formula: Brzycki

Estimated one rep max100

boundary: Brzycki gives 36/36 at one rep

Open this example

Method and limits

What it assumes

A set taken close to failure with good technique.

What it deliberately does not model

Estimates diverge above ten reps and become unreliable.
Technique breakdown under maximal load means the estimate can exceed what is safely liftable.
This is an estimate, not a recommendation to attempt a maximal lift.

Formula version 1.0.0 · definition 1.0.0 · United States · Report a problem with this calculator

Frequently asked questions

How accurate is a one rep max estimate?: Good within a few percent from a set of two to five. Above ten reps the formulas disagree with each other and with reality, because endurance and maximal strength diverge.
Should I test my actual max?: A true maximal attempt carries injury risk and needs technique that holds under load. Most training programmes work from estimates for exactly that reason.