One-Rep Max (1RM) Calculator
Estimate your one-rep max and training percentages from a recent lift.
What Is the One-Rep Max (1RM) Calculator?
One-Rep Max (1RM) Calculator Formula
Epley: 1RM = Weight × (1 + Reps ÷ 30)
Brzycki: 1RM = Weight × 36 ÷ (37 − Reps)
How Is the One-Rep Max (1RM) Calculator Calculated?
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.
One-Rep Max (1RM) Calculator Example
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 the One-Rep Max (1RM) Calculator
Step 1
Enter the weight you lifted and how many reps you completed with good form.
Step 2
Choose kg or lbs.
Step 3
Review your estimated 1RM across three formulas and their average.
Step 4
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.
Common One-Rep Max (1RM) Calculator Scenarios
Scenario 1
Programming strength training percentages (e.g. 5x5 at 80% of 1RM) without testing a true max.
Scenario 2
Tracking estimated strength progress over time using submaximal sets.
Scenario 3
Setting safe starting weights for a new strength program.
Understanding Your Result
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- Retest periodically as you get stronger, since 1RM estimates from old data become outdated.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.
Frequently Asked Questions
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.
What's the difference between the Epley and Brzycki formulas?
Epley scales roughly linearly with reps and can slightly overestimate at higher rep counts, while Brzycki assumes strength drops to zero around 37 reps and tends to be more conservative — both agree closely under about 5 reps.
How do I use the training percentage table?
Multiply your estimated 1RM by a target percentage to get a working weight for a specific goal — lower percentages (60-75%) suit higher-rep hypertrophy work, higher percentages (85-95%) suit max-strength work.
Can I use this for any exercise?
It works best for compound barbell lifts like squat, bench press, and deadlift — it's less reliable for isolation exercises or bodyweight movements.
Why did my estimated 1RM change even though my actual strength didn't?
Because it's recalculated from a fresh submaximal set each time — fatigue, reps performed, and form all shift the estimate, so treat it as an evolving number rather than a fixed one.
Should I trust the average of the formulas more than a single one?
Generally yes — averaging smooths out the bias of any single formula, giving a more balanced estimate when the individual formulas disagree.
How often should I retest my 1RM?
Every 4-8 weeks of consistent training is common — retesting more frequently adds fatigue without providing much new information.
Important Information
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