One Rep Max Calculator
Estimate your 1RM from any set.
Show detailsHide details
Your one-rep max (1RM) is the heaviest weight you could lift once. Testing it directly is risky, so this calculator estimates it from a set you've already completed — then gives you a percentage table for planning training loads.
Loading calculator...
One Rep Max — The Quick Answer
Estimate 1RM from a set with the Epley formula: 1RM = weight × (1 + reps ÷ 30). Lifting 80 kg for 5 reps suggests a 1RM of about 93 kg.
Shortcut
Epley: 1RM = w × (1 + r/30) | Brzycki: 1RM = w × 36/(37 − r)
Reps to percentage of 1RM
| Reps | ≈ % of 1RM |
|---|---|
| 1 | 100% |
| 2 | 95% |
| 4 | 90% |
| 6 | 85% |
| 8 | 80% |
| 10 | 75% |
| 12 | 70% |
Most strength programmes base working weights on percentages of 1RM, so estimating it lets you train the right intensity without maxing out.
How It Works
The Formulas
Three standard estimates
Formula
Epley: 1RM = w × (1 + r/30) Brzycki: 1RM = w × 36/(37 − r) Lombardi: 1RM = w × r^0.10
Variables
Weight lifted
The load you used for the set, in kg or lb.
Reps completed
How many reps you managed at that weight, taken near failure. Most accurate for 1–10 reps.
One-rep maximum
The maximum weight you could lift for a single rep — the basis for training percentages.
Note: These formulas are most accurate for sets of 1–10 reps taken close to failure. Beyond about 15 reps the estimates get unreliable, so the calculator flags very high rep counts.
Worked Example: 100 kg for 5 Reps
Comparing the estimation formulas
Note the weight and reps
100 kg lifted for 5 reps, near failure
Epley: w × (1 + reps ÷ 30)
100 × (1 + 5/30) = 116.7 kg
Brzycki: w × 36 ÷ (37 − reps)
100 × 36/32 = 112.5 kg
Average for a balanced estimate
≈ 116 kg estimated one-rep max
Reference Guide
| % of 1RM | Approx. reps | Weight (1RM = 116 kg) |
|---|---|---|
| 100% | 1 | 116 kg |
| 90% | 4 | 104 kg |
| 80% | 8 | 93 kg |
| 70% | 12 | 81 kg |
| 60% | 20 | 70 kg |
How to Use Your 1RM for Training
Turning the estimate into working weights
Strength plans prescribe weights as a percentage of 1RM, because training effect depends on relative intensity, not absolute load. Roughly: 85–100% builds maximal strength, 67–85% is the hypertrophy range, and below 67% trains muscular endurance.
Best for: Setting the right working weight for your goal
The formulas are most reliable for sets of about 2–10 reps taken close to failure with good form. Beyond roughly 12–15 reps the estimate drifts, because high-rep performance depends on endurance as much as strength.
Best for: Estimating from a hard set of 3–8 reps
If you do test an actual one-rep max, warm up thoroughly, use a spotter or safety bars, and don't do it often — heavy singles are demanding and carry injury risk. For most training, a re-estimated 1RM from your working sets is enough. Not a substitute for coaching.
Best for: Avoiding unnecessary maximal attempts
What Is a One-Rep Max (1RM)?
Your one-rep max is the heaviest weight you can lift for a single repetition of an exercise with good form — the standard benchmark of maximal strength and the reference most training programmes use to set working weights. Testing it directly is demanding and risky, so this calculator estimates it from a normal set using the relationship between weight and reps. It averages several established formulas (Epley, Brzycki, and Lombardi) for a balanced figure, then gives a percentage table so you can read off the loads for strength, muscle-building, or endurance work without ever having to grind out a true maximal single.
Key Features
💡 Pro Tips
- →Estimate from a set of 3–5 hard reps for the best accuracy — low enough to be strength-driven, high enough to be safe.
- →Re-estimate periodically from your working sets instead of testing a true max; a rising estimate means you're getting stronger.
- →Use the percentage table to pick weights: around 80% for 'strength' sets of 5, around 70% for hypertrophy sets of 10.
- →If you do test a real max, warm up in rising singles, use a spotter or safety pins, and never make it a surprise at the end of a hard session.
Common Mistakes
Estimating from very high-rep sets
The formulas lose accuracy beyond about 12–15 reps, where endurance rather than pure strength drives performance. A set of 3–8 reps gives a far more trustworthy estimate.
Treating the estimate as a guaranteed lift
It's a prediction, not a certainty. Grip, technique, fatigue, and the exercise all affect a true max, so warm up and build to any heavy single rather than assuming the estimate.
Programming off absolute weights instead of %1RM
Training intensity is relative. Prescribing a fixed weight suits one lifter and not another; percentages of 1RM scale correctly for everyone, which is why they're the standard.
Research & Citations
Sources and standards referenced for the factual claims on this page
- [1]
Epley, B. (1985). Poundage Chart (origin of the Epley 1RM equation). Boyd Epley Workout, University of Nebraska.
Source of the Epley estimation formula.
View source - [2]
Brzycki, M. (1993). Strength testing — predicting a one-rep max from reps-to-fatigue. Journal of Physical Education, Recreation & Dance, 64(1).
Source of the Brzycki estimation formula.
View source - [3]
National Strength and Conditioning Association (NSCA) (2016). Essentials of Strength Training and Conditioning (4th ed.). Human Kinetics.
Standard reference for training-intensity percentages of 1RM.
View source
This calculator is a reference tool, not a substitute for professional advice. Verify important health, financial, legal, or safety decisions with a suitably qualified professional.
Last updated: October 7, 2026
Creators
Computer Scientist & Developer Tools Author
Reviewers
Technical Reviewer
Table of Contents
Quick Facts
Related Tools
Privacy Guaranteed
Your data never leaves your browser. All calculations are 100% private.
Frequently Asked Questions
How do I calculate my one-rep max?
Use a formula like Epley: 1RM = weight × (1 + reps ÷ 30). If you lift 80 kg for 5 reps, that's 80 × (1 + 5/30) = 93.3 kg. This calculator averages three formulas for a steadier number.
Which 1RM formula should I use?
Epley and Brzycki are the most widely used, and both are reliable for 1–10 reps. Averaging several formulas, as this calculator does, reduces the error from any single one.
How accurate is a 1RM estimate?
For sets of 2–10 reps taken near failure, estimates usually land within a few percent of a tested max. Accuracy drops at very high or very low rep counts, and for beginners or advanced lifters the formulas can drift.
Should I actually test my 1RM?
Only with a spotter, good technique, and a proper warm-up — and not often, since heavy singles are demanding and risky. For most training, an estimate from a 3–5 rep set is perfectly adequate for setting working weights.