Testing a one rep max directly is risky and tiring, so lifters usually estimate it from a set you can already do. This one rep max calculator takes the weight and the reps from a hard set and applies the three formulas coaches trust most, so you can see how much the estimate depends on the method you choose.
What Is the One Rep Max Calculator?
A one rep max, or one rep maximum, is the heaviest weight you can lift for a single repetition. Testing it directly is hard on the body and takes a long time to recover from, so most programs estimate it from a submaximal set instead.
This calculator applies the three formulas that are most commonly used, Epley, Brzycki and Lombardi, so you can see both the answer and how much the choice of method moves it.
How the Formulas Work
Epley: 1RM = w × (1 + r ÷ 30)
Brzycki: 1RM = w × 36 ÷ (37 − r)
Lombardi: 1RM = w × r0.1
All three assume a set taken close to failure and then scale the weight up to what a single rep would allow. They agree closely at lower rep counts and diverge as the reps climb, and they are least reliable beyond about 10 reps, where the curve flattens out.
Getting the Most Out of the Estimate
The accuracy of any estimate depends entirely on how close the set came to failure. A set stopped two reps short of failure can overestimate the maximum by 10 percent or more, while grinding out a true failure set gives a much better read.
Use a consistent method and track the trend rather than the absolute number. If you estimate 150 kilograms one week and 152 the next, the change is more meaningful than either figure, because most of the error comes from the method rather than from your strength.
Training Loads From the Estimate
The percentages in the calculator turn your estimated maximum into working weights. A 90 percent single is a heavy single, 80 percent is a heavy triple or double, 70 percent sits in the hypertrophy range and 60 percent is where most working sets live.
Remember that the percentage is applied to your estimated maximum, so any error in the estimate carries straight through. If your estimate is 10 percent low, then 80 percent of it is really only 72 percent of your true maximum.
Frequently Asked Questions
Which one rep max formula is most accurate?
All three are close at typical working rep counts. Epley is the most commonly used and is a good default, Brzycki is slightly more conservative, and Lombardi produces the lowest figures. The difference is usually under 3 percent at 5 reps.
How many reps should I use for the estimate?
Between 3 and 8 reps is the reliable range. Below 3 reps you get a very demanding set, and above 10 reps the formulas start to diverge sharply and the estimate becomes unreliable.
How close to failure should the set be?
One or two reps short of failure is the target. Stopping short means the formula has to extrapolate further, which is where most of the error comes from.
Should I use the one rep max to program percentages?
Yes, but treat it as a moving target that you re-estimate every few weeks. Using a stale estimate is the most common reason that a percentage-based program feels too heavy or too light.
How often should I test a true one rep max?
Rarely. True max testing carries a real injury and recovery cost, and the improvement in the estimate is small. A heavy single at around 90 percent of your estimated maximum gives useful feedback with much less risk.