One-Rep Max Calculator

Estimate strength without a maximal attempt

Enter the weight lifted and the number of completed repetitions. The calculator applies three common one-repetition maximum equations, shows their average and range, and turns the average into training loads from 50% through 95%.

The result is an estimate for that exercise. It is not a measured maximum and does not transfer from one movement to another.

Three formulas, not one false certainty

The Epley equation is:

1RM = weight × (1 + repetitions ÷ 30)

Brzycki uses weight × 36 ÷ (37 − repetitions), while Lombardi uses weight × repetitions0.1. Each describes the relationship between a submaximal set and a maximum differently.

They agree closely for low repetition counts and spread apart as repetitions rise. The calculator keeps that spread visible because it is information about uncertainty, not noise to hide.

Why low-repetition sets predict better

A set of three or five repetitions is relatively close to maximal strength. A set of fifteen also depends heavily on local muscular endurance, pacing and willingness to continue near failure.

A bench-press study covering 220 men reported strong relationships between repetitions and tested maximum, but advised caution and found errors grew beyond ten repetitions. The calculator accepts up to fifteen so an existing set can still be explored, but warns above ten.

The entered set also needs to be representative. Stopping with several repetitions still available makes every equation underestimate the maximum; degraded technique makes the number difficult to interpret at all.

Training percentages

The percentage table multiplies the averaged estimate by a chosen intensity. If the estimate is 100 kg, 75% is 75 kg and 90% is 90 kg.

A percentage does not determine a complete workout. The number of useful repetitions at 80% varies by exercise and person, and fatigue from earlier sets changes it further. Treat the table as load planning for a program, not as a set-and-repetition prescription.

Estimate versus test

A real 1RM test can be appropriate for experienced lifters in a controlled setting, but it is not necessary simply to produce a training number. A submaximal estimate is often more repeatable and creates less fatigue.

Do not attempt a maximal lift on the strength of this result. Safe testing requires established technique, sensible warm-up and progression, appropriate racks or safety arms, and competent spotting or supervision where the exercise calls for it.

Pain, injury, illness and medical restrictions are reasons to stop and seek qualified guidance rather than reasons to adjust a calculator.

Frequently asked questions

What is a one-rep max?

The heaviest load you can lift once with valid technique for a particular exercise. It is exercise-specific: a bench-press max does not predict a squat or deadlift max.

How does the calculator estimate 1RM?

It applies the Epley, Brzycki and Lombardi equations to the weight and repetitions entered, then shows their average and full range. The disagreement is useful because no equation measures individual repetition endurance exactly.

Which 1RM formula is most accurate?

Accuracy depends on the exercise, repetition count and athlete. A study of bench-press predictions found Brzycki most accurate in its sample, while averaging equations can reduce some error. None is universally best.

How many repetitions should I enter?

A hard set of roughly 2–10 repetitions is the useful range. Research finds prediction error grows above 10 as local muscular endurance contributes more strongly.

Should I test my real one-rep max?

Not merely to verify a calculator. A maximal attempt adds fatigue and injury risk and requires sound technique, suitable equipment, appropriate progression and competent spotting or supervision.

What do the training percentages mean?

They are loads calculated from the averaged estimate. They are planning numbers, not a prescription for sets or repetitions; exercise selection, training age, fatigue and program goals still matter.

Does it matter whether I use kilograms or pounds?

No, provided the unit is consistent. Every formula scales the entered load, and the unit toggle converts the input rather than changing only its label.