Your one-rep max (1RM) is the heaviest load you can lift for a single clean repetition on a given exercise. Finding it directly means working up to a weight you might fail. Most people can get a usable answer from a lighter set instead. Enter the weight you lifted and how many reps you finished, and the calculator estimates your 1RM with three published formulas.
How to get a good input
The estimate is only as good as the set behind it. Use a set taken close to failure, where you could not have done more than one or two extra reps with decent form. A set of 5 that felt like an easy 5 will produce a number that is too low. Stay with sets of 2 to 10 reps. Accuracy falls off above about 10, and the formulas disagree wildly by the time you reach 15 or 20.
Use the same exercise, same range of motion and same pause rules each time, since a bounced bench rep and a paused one are different lifts. Reading across lifts is a common trap: a formula tuned on bench press does not carry over to deadlifts, where all seven equations in a 1997 study underestimated the true max.
The three formulas
Each starts from your weight w and your repetitions r.
Epley: 1RM = w x (1 + r / 30). It comes from a poundage chart in a University of Nebraska training manual (1985) rather than a peer-reviewed study. The rule of thumb is that each extra rep adds about 3.3 percent of the weight.
Brzycki: 1RM = w x 36 / (37 - r). A practitioner article from 1993 is the usual source. You will see it written as w / (1.0278 - 0.0278 x r), which is the same thing with rounded constants. It cannot be used at 37 reps or more, because the bottom of the fraction hits zero.
Lombardi: 1RM = w x r^0.10. It comes from a 1989 weight-training textbook and raises the number of reps to a small power.
For a single rep, all three return the weight you lifted.
Worked example
You squat 225 lb for 5 reps.
Epley: 225 x (1 + 5/30) = 225 x 1.1667 = 262.5 lb.
Brzycki: 225 x 36 / 32 = 253.1 lb.
Lombardi: 225 x 5^0.10 = 225 x 1.1746 = 264.3 lb.
The spread is 11 lb. Which one is right? None of them can know. Use the middle as your planning figure and treat the whole range as honest uncertainty. At exactly 10 reps, Epley and Brzycki give the same answer, so a set of 10 is the one place they agree.
The percentage table
Once you have a 1RM, training plans give loads as a percentage of it. The table below inverts each formula: the percentage of your 1RM that you should be able to lift for a given number of reps. We calculated it from the three equations. It is not copied from a published chart.
| Reps | Epley | Brzycki | Lombardi |
|---|---|---|---|
| 1 | 100% | 100% | 100% |
| 2 | 94% | 97% | 93% |
| 3 | 91% | 94% | 90% |
| 4 | 88% | 92% | 87% |
| 5 | 86% | 89% | 85% |
| 6 | 83% | 86% | 84% |
| 7 | 81% | 83% | 82% |
| 8 | 79% | 81% | 81% |
| 9 | 77% | 78% | 80% |
| 10 | 75% | 75% | 79% |
| 11 | 73% | 72% | 79% |
| 12 | 71% | 69% | 78% |
For a 250 lb max, 5 reps works out to about 214 lb by Epley, 222 lb by Brzycki and 213 lb by Lombardi. The formulas diverge more past 10 reps, which is where the percentages stop being useful.
How accurate is it
Studies that compare predicted and measured 1RM find high correlations, often above 0.9. That sounds reassuring, but a high correlation can coexist with errors of 10 percent or more for an individual. A 1RM set by a direct test is repeatable: a review of 32 studies found a typical day-to-day variation of about 4 percent. The predicted value is less settled, and it depends on the person, the exercise and the rep count.
Estimates are best for upper-body presses, with fewer than 10 reps, in someone who knows how close to failure they were. They suit a first guess at training weights. They are a poor basis for deciding whether to attempt a record, and if you want your actual max, see how to test your one-rep max safely.
Who it does not suit
New lifters often find it hard to judge how close to failure a set was, which makes their estimates unreliable. Anyone with joint or cardiovascular conditions should take professional advice before pushing sets to failure. Lifters who stop sets far from failure will get underestimates. Fatigue, sleep and caffeine move results from one day to the next.
Do not use the estimate for events where a miss has consequences, such as lifting alone without safeties or a spotter.