One Rep Max Calculator (1RM)
Your one rep max is the single strongest number in your training log — it tells you exactly how heavy your sets should be. This free calculator estimates your 1RM from one easy set: enter the weight you lifted and how many reps you completed, and the tool applies four research-backed formulas (Epley, Brzycki, Lombardi and Mayhew), then builds a full training-load table from 50% to 100% of your max.
One Rep Max Calculator
How to Use This Calculator
Choose your unit — kilograms or pounds — then enter how much weight you lifted and how many clean reps you completed. Use the actual weight you handled, not what you think you could lift, and pick a set taken close to failure. Sets of 2 to 10 reps give the most reliable estimates.
Click Calculate and the tool shows your estimated one rep max from four well-known formulas. The Epley estimate leads the results because it is the most widely used in strength sports, but you will see the other three quoted in training apps and programs, so it helps to know how they compare.
The training loads table below the results shows the exact weight to use for every percentage of your new 1RM, from 50% for endurance work up to 100% for max attempts. Plan your next weeks of training straight from the table without doing the arithmetic by hand.
The Formula
All four formulas convert a submaximal set into an estimated 1RM. The headline estimate is the Epley formula: 1RM = w × (1 + r/30), where w is the weight lifted and r is the number of reps. The others are: Brzycki: 1RM = w × 36/(37 − r) — with r = 1 this simplifies to the weight you lifted; Lombardi: 1RM = w × r^0.1; and Mayhew: 1RM = 100 × w / (52.2 + 41.9 × e^(−0.055 × r)).
Worked example: you bench-pressed 100 kg for 5 clean reps. Epley: 100 × (1 + 5/30) = 100 × 1.1667 = 116.7 kg. Brzycki: 100 × 36/32 = 112.5 kg. Lombardi: 100 × 5^0.1 ≈ 100 × 1.175 = 117.5 kg. Mayhew: 100 × 100 / (52.2 + 41.9 × e^(−0.055 × 5)) = 10,000 / (52.2 + 41.9 × 0.7596) ≈ 10,000 / 84.03 ≈ 119.0 kg. All four cluster around 117 kg — and in practice your true max sits within a few percent of that.
Tips
Keep the estimating sets between 1 and 10 reps. Beyond 10 reps the formulas drift for many lifters, so if your program works in the 12–15 rep range, test a heavier, lower-rep set instead and the estimate will be much closer to your true max.
Choose your percentage by goal: 85–95% of 1RM builds pure strength (sets of 1–5), 65–85% builds muscle size (sets of 6–12), and 50–65% builds muscular endurance (sets of 15 or more). Progress by adding small increments — 2.5 kg or 5 lb — week to week rather than jumping weights.
Re-test your 1RM at most every 6–12 weeks. In between, track the estimated 1RM from your working sets in your log: it shows progress without the strain and injury risk of grinding out a true maximum lift.
Frequently Asked Questions
What is a one rep max (1RM)?
Your one rep max is the heaviest weight you can lift for exactly one repetition with good form. Testing it directly is risky without a spotter, so most lifters estimate it from a submaximal set of reps using one of the formulas in this calculator.
How accurate is the Epley formula?
The Epley formula is within about 5% of your true 1RM for most lifters when tested in the 2 to 10 rep range. Accuracy drops at higher rep counts — for sets of 12 or more, treat the estimate as a rough guide only.
How should I warm up before testing my 1RM?
Take 5–10 minutes of light cardio, then do 2–3 warm-up sets with 40%, 60% and 80% of your working weight. Rest 2–3 minutes before each heavy attempt, and always use a spotter when lifting near your maximum.
How often should I test my 1RM?
Once every 6–12 weeks is plenty for most lifters. Testing more often is exhausting and adds injury risk; in between, track the estimated 1RM from your regular working sets instead.
What percentage of my 1RM should I train with?
For strength, work at 85–95% of 1RM in sets of 1–5 reps. For muscle growth, use 65–85% in sets of 6–12 reps. For muscular endurance, use 50–65% in sets of 15 or more. Rotate these phases across weeks rather than mixing everything in one session.
Is the Epley formula accurate for high reps?
The estimate gets less reliable beyond about 10 reps - endurance, not strength, becomes the limiting factor. If your test set is 12+ reps, the calculator may overestimate your 1RM. For a truer number, test with a weight you can lift 3-6 times, or use a 1RM from each rep range as a sanity check.
How often should I retest my 1RM?
Every 8-12 weeks is plenty for most lifters. Max attempts are fatiguing and carry injury risk, so frequent testing trades progress for bragging rights. Between tests, track estimated 1RM from your working sets - if your 5-rep max is climbing, your 1RM is too.
Should beginners test their 1RM?
No - beginners gain strength so fast the number is outdated within a week, and heavy singles with unpracticed technique invite injury. Build technique with 5-10 rep sets for at least 3-6 months, then test if you want. The calculator's rep-based estimate from a comfortable set gives you a starting number without a max-out.