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Strength Calculator

Estimate one-rep max from weight lifted, repetitions, unit, and common strength formulas.

Enter the weight successfully lifted for the rep set.

Use a whole number from 1 to 30. Lower-rep sets are usually more reliable.

Status: initial

Results

Awaiting calculation

One-rep max estimate

Introduction

The Strength Calculator estimates one-rep max from a completed set and shows training loads as percentages of the estimate.

A strength calculator estimates the maximum weight a person might lift for one repetition based on a lighter weight lifted for multiple repetitions.

Formula and method guide

Epley

1RM = weight x (1 + reps / 30)

A common simple estimate for moderate rep ranges.

Brzycki

1RM = weight x 36 / (37 - reps)

A classic one-rep max equation used in many calculators.

Lombardi

1RM = weight x reps ^ 0.10

Provides another perspective on rep-to-max conversion.

Inputs explained

Weight lifted

The load successfully lifted for the full set.

Repetitions

The number of completed reps with proper range and control.

Weight unit

Choose pounds or kilograms. Results stay in the same unit.

Formula

The selected equation used to estimate one-rep max.

Training percentage

A suggested load based on a percentage of estimated 1RM.

FAQs

What does this Strength Calculator do?
It estimates one-rep max from weight lifted and repetitions.
What is one-rep max?
One-rep max, or 1RM, is the estimated maximum weight for one repetition.
Which formula should I use?
Epley is a common default. Comparing formulas can show a reasonable estimate range.
Is the result exact?
No. It is an estimate and can vary by lifter, lift, technique, fatigue, and rep range.
Can I use kilograms?
Yes. Choose kilograms and the result will remain in kilograms.
Can I use pounds?
Yes. Choose pounds and the result will remain in pounds.
Why limit reps to 30?
Very high rep sets usually make one-rep max estimates less reliable.
What is the Epley formula?
Epley estimates 1RM as weight x (1 + reps / 30).
What is the Brzycki formula?
Brzycki estimates 1RM as weight x 36 / (37 - reps).
What is the Lombardi formula?
Lombardi estimates 1RM as weight x reps raised to the 0.10 power.
What is the O'Conner formula?
O'Conner estimates 1RM as weight x (1 + 0.025 x reps).
What are training percentages?
They are loads calculated from a percentage of estimated 1RM.
Can this calculator replace coaching?
No. It is an estimate for planning, not coaching, medical, or safety advice.
Should beginners test one-rep max?
Beginners should be cautious and use qualified coaching before max testing.
Why do different formulas give different results?
Each formula models fatigue and repetitions differently, so estimates naturally vary.

References

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