One Rep Max Calculator (1RM): Estimate Your Max From Any Set
Enter the weight and reps of a hard set to estimate your one rep max, plus a percentage table to pick your training weights. Works in kg or lb.
How the one rep max is estimated
Your one rep max (1RM) is the heaviest weight you can lift once with good form. Testing it for real is tiring and riskier than a normal set, so this calculator estimates it from a set you already did. It runs two well-known formulas and shows the average:
- Epley (1985): 1RM = weight × (1 + reps ÷ 30)
- Brzycki: 1RM = weight × 36 ÷ (37 − reps), first published in Brzycki, 1993
Both formulas give the same number at 10 reps. Below 10, Epley reads a little higher than Brzycki, so averaging the two keeps the estimate in the middle. If you enter 1 rep, the result is simply the weight you lifted.
A worked example
Say you squatted 80 kg for 6 reps (made-up numbers). Epley gives 80 × 1.2 = 96 kg. Brzycki gives 80 × 36 ÷ 31 = 92.9 kg. The average is about 94.5 kg.
The table under the result turns that estimate into training weights. For this example:
% of 1RM | Weight | Approx. reps |
|---|---|---|
90% | 85 kg | 4 |
80% | 75.5 kg | 8 |
70% | 66 kg | 12 |
Round each weight to the plates your gym has.
How to use the result in training
Pick the row that matches the reps in your program and use that weight for your first working set. If the set feels much harder or easier than planned, adjust the next one. Warm up with lighter sets before you get there.
There is no need to test a true max often. Every few weeks, enter a fresh hard set from your normal training and the estimate updates on its own. Writing every set down makes this easy, because you always have a recent set to plug in.
Limits of 1RM formulas
The estimate works best with sets of about 2 to 10 reps taken close to failure. In a study of bench press and leg press, 5-rep sets predicted the 1RM best, and the authors advised using no more than 10 reps in linear equations (Reynolds et al., 2006).
The reps column is an average, not a promise. A meta-regression of 269 studies found that people do more reps on the leg press than on the bench press at the same percentage of 1RM, so tables differ by exercise (Nuzzo et al., 2024). Your own numbers can sit above or below the table. If anything hurts during a set, stop.
Frequently asked questions
How do I calculate my one rep max without maxing out?
Do a hard set of 2 to 10 reps with good form, then enter the weight and the reps. The calculator applies the Epley and Brzycki formulas and shows the average.
How accurate is a 1RM calculator?
It is close enough to plan training when the set had 10 reps or fewer and ended near failure. With more reps, or on exercises like the leg press, the error grows, so treat the number as an estimate.
What percentage of my 1RM should I train at?
It depends on the reps you want. Sets of 6 to 12 reps usually land around 70 to 85% of 1RM, and heavy sets of 1 to 6 reps sit higher; the table under the result shows the weight for each.
Is the Epley or the Brzycki formula more accurate?
Neither wins for everyone. They match at 10 reps and Epley reads slightly higher below that, which is why this calculator averages both.
This is general information, not medical advice. Talk to a professional about your own situation.