One-Rep Max (1RM) Calculator
Estimate your one-rep max and training percentages from a recent lift.
What is it?
This calculator estimates your one-rep max (1RM) — the maximum weight you could lift for a single repetition — from a set performed at a lighter weight for multiple reps, using three widely used strength-training formulas.
Formula
Epley: 1RM = Weight × (1 + Reps ÷ 30)
Brzycki: 1RM = Weight × 36 ÷ (37 − Reps)
Formula Explanation
Each formula estimates how much heavier you could lift for just one rep, based on how many reps you completed at a given weight — more reps at a submaximal weight implies a lower true 1RM relative to that weight. The formulas agree closely for low rep counts (1-5) but diverge more as reps increase, which is why averaging multiple formulas gives a more balanced estimate.
Example Calculation
Lifting 100 kg for 5 reps gives an Epley estimate of 100 × (1 + 5/30) = 116.7 kg, close to the Brzycki estimate of 112.5 kg — averaging to roughly 115 kg.
How to Use
- Enter the weight you lifted and how many reps you completed with good form.
- Choose kg or lbs.
- Review your estimated 1RM across three formulas and their average.
- Use the training percentage table to plan weights for different rep ranges.
Benefits
- Estimates 1RM without requiring you to actually attempt a risky maximal single lift.
- Averages three established formulas for a more balanced estimate than relying on just one.
- Includes a training percentage table for programming different rep ranges off your estimated max.
Use Cases
- Programming strength training percentages (e.g. 5x5 at 80% of 1RM) without testing a true max.
- Tracking estimated strength progress over time using submaximal sets.
- Setting safe starting weights for a new strength program.
What Your Result Means
The estimated 1RM is the heaviest weight you could theoretically lift once with good form, based on your submaximal set. The training percentage table translates that estimate into practical working weights for different training goals — lower percentages for higher-rep hypertrophy work, higher percentages for max-strength work.
Tips
- Estimates are most accurate for sets of 1-10 reps — very high rep sets (15+) produce less reliable 1RM estimates.
- Only use sets taken close to failure with good form — an easy submaximal set will underestimate your true 1RM.
- Retest periodically as you get stronger, since 1RM estimates from old data become outdated.
Common Mistakes
- Using a set that wasn't taken close to failure, which underestimates the true 1RM.
- Relying on estimates from very high-rep sets (15+), where formulas become less accurate.
- Treating the estimated 1RM as exact — always warm up carefully before ever attempting a true maximal lift.
FAQs
How accurate is an estimated 1RM compared to an actual tested max?
It's a reasonable estimate for sets of 10 reps or fewer taken close to failure, but individual factors like fatigue, technique, and muscle fiber type mean it can differ from a true tested max by several percent.
Which formula is most accurate?
No single formula is universally best — Epley and Brzycki are the most commonly used and tend to agree closely for lower rep ranges, which is why averaging them gives a balanced estimate.
Should beginners test their actual 1RM?
Most coaches recommend beginners use estimated 1RM from submaximal sets rather than testing a true max, since proper technique under near-maximal loads takes time to develop safely.
This tool provides an estimate for training programming purposes — always warm up thoroughly and use a spotter or safety equipment before attempting any near-maximal lift.
Last updated: July 26, 2026