One Rep Max Calculator
Estimate the most weight you could lift once, from any set you have already done — with the Epley, Brzycki and Lombardi formulas side by side — then read the load for each rep count and training percentage. Metric and imperial units are both supported.
Estimates are most reliable for sets of 2 to 10 reps — the three formulas differ by about 3% around 5 reps and by much more at high rep counts, so the spread row tells you how much to trust today's number. Brzycki's formula divides by 37 minus your reps, which is why no calculator should use it beyond about 25 reps. A measured 1RM with a spotter is still the only way to know the real figure.
Formula and calculation
Worked example
You bench 80 kg for 8 reps. Epley gives 80 × (1 + 8 ÷ 30) = 101.3 kg, Brzycki 80 × 36 ÷ 29 = 99.3 kg, and Lombardi 80 × 8^0.10 = 98.5 kg — a three-formula average of 99.71, with the formulas 2.85% apart. Read down the rep table and 5 reps is about 88.9% of that average, so a set of 5 would call for roughly 89 kg.
What to do with the number
The point of a 1RM estimate is programming, not bragging. Most strength plans are written as percentages of it: five sets of five around 80%, triples near 87%, heavy singles at 90% or above. The percentage table above turns your estimate into those loads, and the rep table does the reverse — telling you what a 5RM or 8RM should feel like. Treat the result as a moving target: it drifts with sleep, food and fatigue, so test with a real max only occasionally and re-estimate from a hard set of three to six reps in between. On a cut, expect the number to fall while your strength is actually being maintained — that is normal. Always leave a rep or two in reserve on anything over 90%, and use a spotter or safety pins for the real thing.
What the results mean
- Estimated one-rep max
- Your estimated one-rep max in kilograms — the average of the three formulas. It is the most you could lift once with good form on a fresh day, and it is an estimate: only a real, spotted max attempt measures it.
- Epley (1985)
- The Epley formula's estimate in kilograms. It reads about 1–4% higher than the others at 2 to 9 reps, so it is the optimistic one of the three.
- Brzycki (1993)
- The Brzycki formula's estimate in kilograms. It agrees with Epley at one rep and at ten, and reads higher than both Epley and Lombardi above about 12 reps. Its divisor (37 minus your reps) shrinks to zero at 37 reps, so it is the reason high-rep estimates are unreliable.
- Lombardi (1989)
- The Lombardi formula's estimate in kilograms. It uses a power curve, so it behaves differently again — the three numbers together show how much the answer depends on which equation you picked.
- One-rep max in pounds
- The same three-formula average in pounds.
- Spread between the formulas
- How far apart the three formulas landed, as a percentage of the average. Under about 5% means the set was in the range they are built for; double digits means you are past the range where any of them is trustworthy.
Frequently asked questions
How accurate is a one-rep-max estimate?
For a set of 2 to 10 reps on a big compound lift, published comparisons usually land within about 5% of a measured 1RM — a few kilograms either way. The estimate is least reliable for isolation exercises, for beginners still learning technique, and for high-rep sets where muscular endurance starts to matter more than strength.
Which formula is most accurate?
There is no single winner. Studies that compare them find Epley and Brzycki slightly overestimate above about 8 reps, Mayhew and Wathen often do best in specific lifts, and the ranking changes between bench, squat and deadlift. Averaging several formulas cancels out each one's bias, which is why this page leads with the average.
Can I estimate my 1RM from a set of 20 reps?
You can, but do not trust it. Above roughly 15 reps the differences between people's endurance dominate the formula, and the three estimates on this page can spread 20% or more. If you need a number, use a hard set of 3 to 6 reps instead — it costs less recovery and predicts better.
Should I actually test my one-rep max?
Only if you have a reason to compete or program around it, and only after a proper warm-up with a spotter or safety pins. A true max attempt costs several days of recovery and carries real injury risk if form breaks down. Re-estimating from a hard set of 3 to 6 reps every few weeks and testing a true max a few times a year is plenty for most lifters.