One Rep Max Calculator — 3 Formulas + % Table

The Formula

The One Rep Max (1RM) is the maximum weight you can lift for a single repetition. It is estimated from sub-maximal lifts because testing a true 1RM carries injury risk. Each formula was developed on different populations and gives slightly different results.

Variable Definitions

How to Use This Calculator

1. 1

   Enter the weight you lifted (in lbs or kg — output matches input unit).

2. 2

   Enter the number of reps you completed with that weight (capped at 15 for accuracy).

3. 3

   Select your preferred formula — Epley is the most common.

4. 4

   Use the percentage breakdown table to plan your training loads.

5. 5

   Click through different formulas to see how much estimates vary — this helps you choose the right formula for your training style.

Common Applications

• Strength training program design — calculate training loads at specific percentages of 1RM (65-85% for hypertrophy, 85-93% for strength) for programs like 5/3/1 or Starting Strength
• Progress tracking — estimate 1RM from sub-maximal sets over time to measure strength gains without repeatedly testing maximal lifts and risking injury
• Plateau breaking — use multiple formulas (Epley, Brzycki, Lombardi) to identify the most accurate estimate for your rep range and adjust training loads accordingly
• Injury-safe strength assessment — estimate max strength from sets of 3-8 reps rather than attempting a true 1RM, which carries higher injury risk without a spotter

As reps increase, the percentage of your 1RM decreases: 1 rep = 100%, 12 reps = 70%

Understanding the Concept

Estimated 1RM formulas allow you to calculate your max strength from sub-maximal sets, reducing injury risk. Accuracy decreases as rep count increases — sets of 3–8 reps give the best estimates. Above 10 reps, all formulas become less reliable because neuromuscular fatigue and technique breakdown affect performance more than raw strength. The percentage breakdown table (50–100%) lets you plug the numbers directly into popular programs like 5/3/1 (Jim Wendler), Starting Strength (Mark Rippetoe), Smolov, or periodized block programming. Most programs prescribe sets at 65–85% of 1RM for volume work (hypertrophy and muscular endurance), 85–93% for pure strength work, and 93%+ for peaking. A practical example: if your estimated bench press 1RM is 225 lbs, then 75% = 169 lbs (hypertrophy sets of 8–12 reps), 85% = 191 lbs (strength sets of 5–8 reps), and 90% = 203 lbs (peak strength sets of 3–5 reps). The Brzycki formula gives the most conservative (safest) estimates and is recommended for beginners to avoid overestimating and attempting weights beyond their actual capability. Epley is the standard for intermediate and advanced lifters. For older adults or those rehabbing from injury, Brzycki is preferred because it provides a margin of safety. For powerlifters testing peaking cycles, Lombardi or Epley are more commonly used. Regardless of formula, the standard error of estimate is approximately ±3–5%, so always add a safety margin when attempting heavy weights. Never attempt a true 1RM for an exercise you have not been training with proper form for at least 6 weeks.

Frequently Asked Questions

Sources & References