How do you calculate one rep max?

Enter the weight and repetitions from a technically sound hard set. Prediction equations estimate the single-repetition maximum; this page compares four equations and reports their average and spread.

Is an estimated 1RM exact?

No. Accuracy varies with the exercise, repetition count, technique, training status, and how close the set was to true effort.

Should beginners test a true one-rep max?

A submaximal estimate avoids deliberately attempting a maximal lift. Beginners should prioritize technique and qualified supervision.

Calculating One Rep Max

Estimate your one-repetition maximum from a completed set, compare four established formulas, and turn the result into practical training loads.

Written and checked by TheToolNet Editorial Team · Last reviewed: October 2, 2026 · Editorial method

Strength-training safety warning

This calculator cannot assess your technique, medical history, equipment, or readiness. The numbers may be inaccurate and are not medical or coaching advice. Consult a doctor before strenuous lifting if you have a health condition, symptoms, are pregnant, or have been advised to limit exercise. Use suitable safety equipment and qualified supervision; stop for pain, dizziness, chest pain, or unusual breathlessness.

Direct answer

Estimated 1RM = formula applied to lifted weight and completed repetitions

One-rep max estimator

How the estimate is calculated

The calculator compares Epley, Brzycki, Lombardi, and Mayhew estimates. For 100 kg lifted five times, the formulas do not return exactly the same answer; that disagreement is useful evidence that 1RM is a range, not a precise measurement.

Published validation work shows that equation accuracy depends on repetition count and exercise. A bench-press validation study found better validity at lower repetition counts, while a comparison of seven equations documents the formulas and their exercise-specific differences.

Use the number responsibly

Use a recent set performed with consistent range of motion and sound technique.
Prefer a hard set of roughly two to eight repetitions; high-repetition estimates depend more on endurance.
Treat the formula spread as uncertainty rather than choosing the largest number.
Round training loads to plates you can load safely and conservatively.

Frequently asked questions

Can this calculate a bench, squat, deadlift, or leg-press max?

Yes, but keep estimates exercise-specific. A bench-press set estimates bench press, not squat or deadlift.

Why limit the input to 12 repetitions?

Prediction error generally grows as the set moves farther from maximal strength and becomes more affected by local muscular endurance.

Is the average formula always best?

No. It is a transparent summary. Your history with a particular equation and lift may make one formula more useful for trend tracking.