How to calculate your one-rep max (1RM)
Your one-rep max is the most weight you can lift once. You can estimate it safely from a lighter set with a simple formula, no scary max-out needed. Here is the maths and how to train with it.
Estimate the most you could lift for a single rep from a set you have already done.
Your one-rep max, or 1RM, is the heaviest weight you can lift for a single clean repetition of an exercise. It is the number strength programs are built around, but actually testing it means grinding out an all-out single, which is risky and only worth it for experienced lifters. The smarter way is to estimate it from a set you can already do for several reps, using a simple formula. Here is how to calculate your one-rep max, the two main formulas, and how to turn the number into training weights. This is general fitness information, not medical or coaching advice.
In short: do a set to near failure with a weight you can lift for 2 to 10 reps, then plug the weight and reps into a formula. The Epley formula is 1RM = weight x (1 + reps / 30). A free one-rep max calculator runs it instantly and shows your training percentages.
What a one-rep max is (and why you estimate it)
1RM is the standard measure of maximal strength for a lift, usually the big barbell movements: squat, bench press, deadlift and overhead press. Coaches use it to set training loads, because most programs prescribe work as a percentage of your 1RM (for example "5 sets of 3 at 80 percent").
The problem is that a true one-rep max attempt is demanding and carries injury risk, especially without a spotter and good technique. So unless you are a competitive lifter peaking for a test, you estimate 1RM from a lighter, safer set. The estimate is reliable as long as the set is hard and the reps are reasonably low.
The two main formulas
There are several rep-max formulas, but two dominate, and they agree closely at low reps:
- Epley: 1RM = weight x (1 + reps / 30)
- Brzycki: 1RM = weight x 36 / (37 - reps)
Worked example: you bench 100 kg for 5 reps. Epley gives 100 x (1 + 5/30) = 100 x 1.1667 = 116.7 kg. Brzycki gives 100 x 36 / (37 - 5) = 100 x 36/32 = 112.5 kg. The two land within a few kilos, which is typical. They give the exact same answer at 10 reps (both 133 kg here). Below 10 reps Epley reads a touch higher; above 10 reps Brzycki reads higher and the gap widens quickly, and Brzycki breaks down near 37 reps, so neither should be trusted for long sets. Use whichever your program or calculator favours; the difference is small where it matters, at low reps.
The same works in pounds: 225 lb for 5 reps gives an Epley estimate of 225 x 1.1667 = about 262 lb.
Keep the reps low for accuracy
The single most important rule: estimate from a low-rep set. These formulas are accurate for sets of roughly 10 reps or fewer. Beyond that, fatigue, grip and breathing start to limit you before your muscles truly do, so a 20-rep set gives an unreliable estimate. The sweet spot is a genuinely hard set of 3 to 6 reps: heavy enough to be honest, light enough to be safe. And the set must be close to failure. Close to failure means a set you could barely repeat, not one you grind out with failing form. If you stop with three reps left in the tank, the estimate will read low. If you track effort, reps in reserve (RIR) helps: a set of 5 that still had 2 reps left is really closer to a set of 7, so estimate from 7 reps, not 5.
Training with percentages of your 1RM
Once you have a 1RM, programs prescribe loads as a percentage of it. Rough training zones:
| Goal | Reps | Percent of 1RM |
|---|---|---|
| Max strength | 1 to 5 | 85 to 100 percent |
| Muscle growth (hypertrophy) | 6 to 12 | 70 to 85 percent |
| Muscular endurance | 15 and up | under 65 percent |
These zones are conventions, not hard lines; research shows similar muscle growth across a wide load range when sets are taken close to failure. You can also read it the other way, as roughly how many reps a given percentage allows:
| Percent of 1RM | Reps you can usually do |
|---|---|
| 100 percent | 1 |
| 95 percent | 2 |
| 93 percent | 3 |
| 90 percent | 4 |
| 87 percent | 5 |
| 85 percent | 6 |
| 80 percent | 8 |
| 75 percent | 10 |
| 70 percent | 12 |
This is an average. How many reps you manage at a given percentage varies by lift and by person, and lower-body lifts often allow more reps than upper-body ones.
So if your estimated bench 1RM is 116 kg and your program calls for 80 percent, you would load about 116 x 0.80 = 93 kg for your working sets. Our percentage calculator does the percentage maths if you want to build your own chart.
Estimate each lift separately
A big mistake is assuming one 1RM covers everything. Your squat, bench, deadlift and press each have their own one-rep max, often very different, because they use different muscles and leverages. Most people deadlift the most and overhead press the least. A 140 kg squat for 5 reps, for example, gives about 163 kg by Epley, which has nothing to do with your bench number. Deadlifts are often the least accurate to estimate, because grip fatigue can stop the set before your legs and back are truly done. Estimate and track each lift on its own, and re-estimate every few weeks as you get stronger.
A safety note
An estimated 1RM is a programming tool, not a number to go and test for the sake of it. Do your estimating set with a spotter or safety bars, stop the moment your technique breaks down, and leave a rep or two in reserve if you are new to the lift, since poor technique is the main cause of both bad estimates and injuries. If you do ever attempt a true max, warm up with progressively heavier sets (for example roughly 50 percent for 5 reps, 70 percent for 3, then 85 percent for 1) and take small jumps. For most people, training off the estimate is safer and works just as well. Stop any set that causes sharp pain, and if you are new to lifting, returning from injury, or have a heart or blood-pressure condition, get guidance from a qualified coach or doctor first.