One rep max (1RM) calculator
Enter a weight and how many reps you lifted it for, and this calculator estimates your one rep max: the heaviest weight you could lift once. It averages the two standard formulas, Epley and Brzycki, and turns the result into a training percentage table. Works for bench press, squat, deadlift and any other barbell lift.
| % of 1RM | Weight | Typical reps |
|---|---|---|
| 95% | — | 2 |
| 90% | — | 3–4 |
| 85% | — | 5–6 |
| 80% | — | 7–8 |
| 75% | — | 9–10 |
| 70% | — | 11–12 |
| 65% | — | 13–15 |
| 60% | — | 16+ |
Estimates are most reliable for sets of 2 to 10 reps taken close to failure. Above 12 reps the formulas overestimate. Never attempt a true max without a spotter or safeties.
What is a one rep max?
A one rep max (1RM) is the heaviest weight you can lift for a single repetition of an exercise with proper form. It is the standard measure of maximal strength, and most strength programs prescribe working weights as a percentage of it. You do not need to test it under a bar: a hard set of 2 to 10 reps predicts it accurately.
How the calculator works
The calculator runs your set through the two most widely used estimation formulas and shows their average, which in practice tracks tested maxes better than either formula alone:
The two agree almost exactly up to 5 reps and drift apart as reps climb: Epley reads higher, Brzycki more conservative. If a program tells you which formula it assumes, use that number from the line under the result instead of the average.
Using your 1RM in a program
Percentages of 1RM map to training goals. Heavy sets at 80 to 90% build maximal strength, moderate sets at 65 to 80% are the main zone for muscle growth, and lighter work below 65% suits technique, speed and warm-ups. The table above converts your estimate into those loads, and the warm-up sets calculator ramps you up to them safely.
In the APX app you do not manage this by hand: log a set once and the app knows your working weights, shows what you lifted last time and keeps your plan honest. The calculator is the manual version of what your AI workout plan does on every exercise.
Method and sources
This calculator is not a proprietary algorithm: it runs two published equations from the strength-training literature, and the percentage table follows load ranges established in meta-analytic research. The sources are listed so you can check the math yourself.
Both equations are estimates derived from group data. They are most accurate for sets of 2 to 10 reps taken close to failure and drift upward at higher rep counts. Individual results vary with training experience, the lift and technique.
- Epley B (1985). Poundage Chart. Boyd Epley Workout. Body Enterprises, Lincoln, NE (print source) Used for: the Epley formula, 1RM = weight × (1 + reps / 30)
- Brzycki M (1993). Strength Testing: Predicting a One-Rep Max from Reps-to-Fatigue. Journal of Physical Education, Recreation & Dance, 64(1), 88–90 Used for: the Brzycki formula, 1RM = weight × 36 / (37 − reps)
- Schoenfeld BJ, Grgic J, Ogborn D, Krieger JW (2017). Strength and Hypertrophy Adaptations Between Low- vs. High-Load Resistance Training: A Systematic Review and Meta-analysis. Journal of Strength and Conditioning Research Used for: the load ranges in the percentage table: heavy loads for strength, moderate loads for growth
Frequently asked questions
Estimates from sets of 2 to 10 reps are typically within about 5% of a tested max for trained lifters. Accuracy drops as reps go up, so a 5-rep set predicts your max better than a 12-rep set. Formulas also differ slightly: Epley runs a little higher than Brzycki at higher reps, which is why this calculator shows both.
Use a hard set of 3 to 6 reps taken close to failure. That range is heavy enough to reflect true strength but not so long that fatigue distorts the math. A recent working set from your log works fine, as long as you could not have done more than one or two extra reps.
Usually no. A true max attempt requires solid technique under heavy load and a spotter. For most people an estimated 1RM from a rep calculator is safer and accurate enough to set training percentages. Test a real max only when you have months of consistent technique work behind you and a reason to need the exact number.
Programs prescribe working weights as percentages of 1RM. As a rule of thumb: strength work sits at 80 to 90% for 3 to 6 reps, muscle growth at 65 to 80% for 6 to 12 reps, and technique or speed work below 65%. The percentage table under the calculator converts your estimated max into those working weights.
Whenever your working sets change meaningfully, roughly every 4 to 8 weeks in a consistent program. If you logged 5 clean reps at a weight that used to be your 3-rep max, your 1RM has gone up and your percentages should follow.
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