One Rep Max Calculator
Estimate your one-rep max (1RM) using the Epley formula, plus suggested training weights for common rep ranges.
For best accuracy, use a rep range of 1-15. Estimates get less reliable at higher rep counts.
This is an estimate for training planning only, not medical or professional coaching advice. Always use proper form and a spotter when testing near-max weights.
How is one-rep max calculated?
This calculator uses the Epley formula, one of the most widely used methods in strength training to estimate a one-rep max (1RM) — the heaviest weight you could theoretically lift for a single rep — without you actually having to attempt a maximal lift. The formula is: one-rep max = weight lifted × (1 + reps ÷ 30). For example, lifting 135 lbs for 8 reps estimates a 1RM of about 171 lbs. This lets lifters gauge their strength progress and plan programming without the injury risk of testing a true 1RM directly.
Why does the rep range matter?
The Epley formula, like all 1RM estimation formulas, is most accurate in the 1-10 rep range and becomes progressively less reliable above about 12-15 reps, since very high-rep sets are influenced more by muscular endurance and fatigue tolerance than by pure maximal strength. If you enter a rep count above 15, treat the resulting estimate with extra caution — different formulas (like Brzycki or Lombardi) can produce noticeably different numbers at higher rep counts.
How do I use my one-rep max for training?
Most strength programs prescribe working weights as a percentage of your 1RM rather than always training at max effort. Lower percentages (60-75%) with higher reps build muscular endurance and hypertrophy, moderate percentages (75-85%) with moderate reps build strength and size, and higher percentages (85-95%+) with low reps build maximal strength and power. This calculator's breakdown shows suggested working weights at 65%, 75%, 85%, and 95% of your estimated 1RM so you can plan sets without recalculating percentages by hand.
Frequently Asked Questions
What formula does this one-rep max calculator use?
It uses the Epley formula: one-rep max = weight lifted × (1 + reps ÷ 30). It's one of the most commonly used formulas in strength training for estimating 1RM from a submaximal set.
How accurate is an estimated one-rep max?
It's a solid estimate, especially in the 1-10 rep range, but it's not a substitute for an actual tested max. Individual fatigue tolerance, technique, and muscle fiber composition can all cause your real 1RM to differ somewhat from the formula's prediction.
Why shouldn't I use very high rep counts in this calculator?
Formulas like Epley become less accurate above roughly 12-15 reps because high-rep sets are driven more by muscular endurance than maximal strength, which skews the estimate. Keep your test set in the 1-15 rep range for the most reliable result.
Is it safe to test my actual one-rep max?
Testing a true 1RM carries more injury risk than submaximal training, especially without a spotter or proper warm-up. Many lifters prefer estimating 1RM from a comfortable rep range instead, which is exactly what this calculator is designed for.
How do I use the percentage breakdown for programming?
Lower percentages like 65-75% with more reps are typically used for hypertrophy and endurance work, while higher percentages like 85-95% with fewer reps target maximal strength and power. Use the breakdown weights as a starting point for programming your sets.
Does this work for any exercise, like squat, bench, or deadlift?
Yes — the Epley formula is exercise-agnostic and works the same way whether you're estimating your bench press, squat, deadlift, overhead press, or any other barbell lift.
Can I use kilograms instead of pounds?
Yes. The formula works with any consistent unit — enter your weight in kg and the result and breakdown will simply be in kg as well.
Why do different one-rep max calculators give different results?
Several formulas exist (Epley, Brzycki, Lombardi, and others), each derived from different data sets and assumptions. They tend to agree closely at low reps but diverge more at higher rep counts, which is why this calculator recommends staying in the 1-15 rep range.