One-Rep Max Calculator
Estimate your one-rep max from any submaximal lift using the Epley formula.
How to use
- Enter the weight you lifted and how many clean reps you did.
- Click Calculate to get your estimated 1RM and a percentage table.
- Use the table to plan your training loads.
For information only — not medical advice. Consult a healthcare professional for personal guidance.
What Is a One-Rep Max Calculator?
Your one-rep max (1RM) is the heaviest weight you can lift once with good form. It is the reference point for nearly all strength programming — prescriptions like "5 sets at 80% of 1RM" are meaningless without it. Testing a true max, however, is fatiguing, time-consuming, and the riskiest way to lift. This calculator estimates your 1RM from a submaximal set instead: enter a weight you lifted and the clean reps you completed (between 1 and 12), and it projects your max using the Epley formula.
The relationship between reps and percentage of max is remarkably consistent across lifters: a weight you can lift for 5 reps is roughly 85–87% of your max, 8 reps about 80%, 10 reps about 75%. Estimation formulas are just these relationships written as algebra, fitted from decades of strength research and coaching practice.
How to Use the One-Rep Max Calculator
- Enter the weight you lifted, in kilograms or pounds.
- Enter the number of full, good-form repetitions you completed (1–12) — ideally from a recent set taken close to failure.
- Click Calculate to see your estimated one-rep max for that lift.
- Use the estimate to set training loads by percentage, and re-test with a fresh set every training block or two.
The Epley Formula
Developed by Boyd Epley, founder of the Nebraska strength program, the formula is: 1RM = weight × (1 + reps ÷ 30). A 100 kg lift for 6 reps gives 100 × 1.2 = 120 kg. The formula is most accurate in the 2–10 rep range; beyond about 10 reps, endurance and technique contribute more, and estimates inflate. It also behaves slightly differently per lift — deadlift estimates from high reps tend to overshoot, bench press estimates are usually close — which is why experienced lifters calibrate any formula against at least one known performance on each main lift.
Tips for Using Your Estimated Max
- Use a "training max" of 90–95% of the estimate for percentage-based programs — it leaves room for bad days and keeps bar speed honest.
- Only count sets with full range of motion and no assistance; spotted or bounced reps corrupt the input and inflate the estimate.
- An estimate from a set stopped two reps before failure will read low — the formula assumes the set was near your limit.
How accurate is a calculated 1RM?
For sets of 2–8 good reps, Epley estimates usually land within about 2–5% of a tested max for common barbell lifts. Errors grow with higher reps and with lifts where technique or grip fails before strength does. For programming purposes that accuracy is plenty — training loads are routinely adjusted by feel within a wider band than the formula's error.
Should beginners test their one-rep max?
Generally no. New lifters gain strength so quickly that any max is outdated within weeks, and their technique under maximal load is exactly what is still being learned. A 3–5 rep set estimated through this calculator gives a safer, equally useful number. Save true max attempts for experienced lifters, ideally supervised, after a structured peak.
Why do different calculators give me different maxes?
Because Epley is not the only fitted equation — Brzycki, Lombardi, and others curve the reps-to-percentage relationship slightly differently, especially at high reps. At 3–5 reps they nearly agree; at 10–12 reps they can differ by several percent. Pick one formula and stick with it so your progress tracking stays comparable over time.
What percentage should I use for sets of 8?
Around 80% of 1RM is the classic answer for sets of 8 near failure, with 75% suiting higher-volume work where later sets fatigue. Individual variation is real — some lifters are "fast-twitch" and manage fewer reps at a given percentage. Track your own reps-at-percentage on main lifts; after a few sessions your personal table beats any generic chart.