Quick answer: One-repetition maximum (1RM) is the heaviest weight you can lift once with good form. This 1RM calculator estimates it safely from a lighter set: enter the weight and reps you managed, and it averages six proven formulas — Epley, Brzycki, Lombardi, Mayhew, O'Conner and Wathan — then converts the result into training percentage loads from 90% down to 50%.
Last reviewed: September 2026
Key facts
- A 1RM is the heaviest single lift you can complete with proper form.
- The Epley formula is the simplest and most widely used.
- Estimates land within about 5-10% of a true tested max.
- Training percentage loads turn your 1RM into daily working weights.
This free one rep max calculator estimates your 1RM from any set of 1-12 reps, averaging six formulas and converting to a training percentage table.
How to use this 1RM calculator
- Enter the weight you lifted and pick kg or lb.
- Enter reps completed (1-12).
- Read your estimated 1RM.
- Use the training percentage table for working weights.
The six 1RM formulas
Formulas include Epley, Brzycki, Lombardi, Mayhew, O'Conner and Wathan.
Frequently asked questions
Which 1RM formula is the most accurate?
No single formula wins everywhere. The Epley formula is most widely used. Averaging several formulas gives the most honest estimate.
Can I use this for reps above 10?
Use caution above 10 reps. Brzycki is invalid past 10 reps. Retest with heavier weight for 3-6 reps.
Why do formulas give different numbers?
Each uses different math models. The average is more reliable than any single formula.
Is it safe to attempt my estimated 1RM?
Use proper safety equipment and spotters. Many lifters train off estimates without maxing out.
How often should I retest?
Every 8-12 weeks is typical.
What is a training percentage table?
It converts your 1RM into working weights for each session.
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