Use the free One Rep Max Calculator below: your data never leaves your browser — all work happens on your device, and nothing is uploaded to any server.
What This Calculator Does
A one rep max calculator estimates the heaviest weight you could lift for a single repetition, without you having to attempt it. In strength training, that single-rep maximum is called your 1RM. Coaches use it to set training loads: for example, a program might ask for 5 sets of 5 reps at 80 percent of your 1RM. Testing a true 1RM is risky and tiring, especially for beginners, because it demands perfect form under a maximal load. Estimating it from a lighter set is safer and still useful.
This tool uses two well-known formulas and averages them. The Brzycki formula divides the weight by 1.0278 minus 0.0278 times the reps. The Epley formula multiplies the weight by 1 plus reps divided by 30. Both were built from lifting data and agree closely for low rep counts. The tool also converts the average into training loads at 90, 80, 70, and 60 percent, so you can plan sets right away. These are estimates, not guarantees, and your real 1RM on a given day depends on sleep, fatigue, technique, and the lift itself.
How to Use It
Type the weight you lifted and how many clean repetitions you completed. Count only reps with good form; a half rep does not count. Click Calculate. You will see the Brzycki estimate, the Epley estimate, their average, and the percentage loads. Use the average for programming, but round to weights your gym actually has. If your gym uses 2.5-kilogram plates, a load of 73.4 kilograms becomes 72.5 or 75 in practice. Re-test every four to eight weeks, or whenever a program block ends, so your loads keep pace with your strength.
The Formulas, Explained
Both formulas assume that as reps rise, the weight you can handle falls in a predictable curve. Brzycki’s curve drops a little faster, while Epley’s is a straight-line rise with reps. For a set of 5 reps at 80 kilograms, Brzycki gives about 89.9 kilograms and Epley gives about 93.3 kilograms, averaging about 91.6. For a set of 10 reps, the gap widens slightly, which is why estimates from sets above 10 reps are less trustworthy. The formulas also assume you went close to failure. A set of 5 reps where you could have done 5 more will understate your true maximum.
A Worked Example
Suppose you bench pressed 60 kilograms for 8 reps. Brzycki gives 60 divided by (1.0278 minus 0.2224), which is about 74.5 kilograms. Epley gives 60 times (1 plus 8 divided by 30), which is 76 kilograms. The average is about 75.3 kilograms. Your training loads would be about 67.7 kilograms at 90 percent, 60.2 at 80 percent, 52.7 at 70 percent, and 45.2 at 60 percent. Notice that your 8-rep weight sits near 80 percent, which matches the usual guide that 8 reps correspond to roughly 80 percent of 1RM. That cross-check is a good sign the estimate is sensible.
Common Mistakes
The most common mistake is using a high-rep set, such as 20 reps, and treating the estimate as precise. It is not. Another is using a weight from a machine to predict a barbell lift, or vice versa; different equipment changes the lift. A third is testing 1RM too often. True max attempts are stressful and can stall progress if repeated weekly. Use estimates for programming and save real max tests for the end of a training block, with a spotter, good warm-up, and a coach if you are new to the lift.
Frequently Asked Questions
Does it work for every lift? It works best for barbell squats, bench presses, deadlifts, and overhead presses. It is weaker for single-joint lifts like curls, where small muscles fatigue differently. Should beginners use it? Yes, with light weights and strict form, because it avoids risky max attempts. What if the two formulas disagree a lot? That usually means the rep count was high or the set was not near failure. Re-test with a heavier weight and fewer reps.
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