---
title: One Rep Max Calculator (1RM) with Percentage Chart
url: https://progresslens.app/tools/one-rep-max-calculator/
language: en
updated: 2026-11-13
---

# One rep max calculator

Estimate your one-rep max from a set you’ve done, without testing a true max, and get training weights for every percentage.

Short answer

Estimated 1RM = weight × (1 + reps ÷ 30) (Epley). For example, 100 kg for 5 reps is about 115 kg. This calculator averages three formulas and gives a percentage chart for training.

Calculated in your browser. Nothing you enter is sent anywhere.

## Formulas

Epley: weight × (1 + reps ÷ 30). Brzycki: weight × 36 ÷ (37 − reps). Lombardi: weight × reps0.1. We show the average. Estimates are best from sets of 3–6 reps close to failure and get less reliable above 10.

## Strength on a cut

If your estimated 1RM holds or climbs while your weight drops, you’re almost certainly keeping your muscle. Log it next to your waist and photos every few weeks.

## See how far you’ve come.

Take a check-in, tap AI Analyze and get your Progress Report: body-fat range, what changed, fat or muscle, and whether to cut or bulk. On iPhone, iPad and Android, with no account. Your photos stay on your phone.

FAQ

## Frequently asked questions

**How accurate is a 1RM calculator?**

Usually within about 5% for sets of up to 6 reps taken close to failure. Higher-rep sets and less experienced lifters see bigger errors.

**Should I test my real one rep max?**

You don’t need to. An estimate from a hard set of 3–5 is safer and good enough for planning training.

**What percentage of 1RM builds muscle?**

Anything from about 30% to 85% builds muscle if sets are taken close to failure; 65–85% (6–12 reps) is the most common range.

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ProgressLens is an AI progress photo app for iPhone, iPad and Android that turns your check-in photos and tape measurements into a Progress Report: your body-fat range, what changed, whether you are losing fat or muscle, and whether to cut, lean bulk, recomp or maintain.
App Store: https://apps.apple.com/app/progresslens/id6806300575
Google Play: https://play.google.com/store/apps/details?id=app.progresslens