One-Rep Max (1RM) Calculator
Enter the weight you lifted and how many reps you completed to estimate your true one-rep max (1RM). The calculator averages the Epley and Brzycki formulas, the two most widely used methods in strength training.
How this calculation works
The Epley formula estimates 1RM as weight × (1 + reps ÷ 30). It is simple, slightly favors higher rep counts, and is the formula most barbell apps default to.
The Brzycki formula estimates 1RM as weight × 36 ÷ (37 − reps). It tends to run a touch lower than Epley at moderate rep ranges and is undefined at 37+ reps, so above that the calculator falls back to Epley alone.
Your result is the average of both formulas (or the raw weight if you entered exactly 1 rep, since a single rep already is your max). Averaging two independently-derived formulas smooths out the quirks of either one alone.
Worked example
Training percentages from your 1RM
Once you know your estimated 1RM, most strength programs prescribe work sets as a percentage of it. Typical rep ranges at each percentage look like this:
| % of 1RM | Typical reps | Common use |
|---|---|---|
| 100% | 1 | Max-effort test |
| 95% | 2 | Peaking / strength |
| 90% | 4 | Strength |
| 85% | 6 | Strength-hypertrophy |
| 80% | 8 | Hypertrophy |
| 75% | 10 | Hypertrophy |
| 70% | 12 | Hypertrophy / endurance |
Why accuracy drops at higher reps
Both Epley and Brzycki assume a roughly linear relationship between reps and fatigue. That assumption holds reasonably well up to about 10 reps, but beyond that muscular endurance and lactate tolerance start to matter as much as maximal strength, so the formulas increasingly overestimate or underestimate depending on the lifter. If you regularly train in the 12–20 rep range, treat any 1RM estimate from those sets as a rough ballpark rather than a number to program against.
Warm up before testing or estimating
- Start with 2–3 general warm-up sets at very light weight to raise core temperature and rehearse the movement pattern.
- Work up in weight over 3–4 sets, dropping reps as the load increases, until you reach the working weight you plan to estimate from.
- Stop the working set at or just short of technical failure — form breakdown before failure makes the rep count unreliable.
- Rest 2–5 minutes between heavy sets so fatigue from a previous set doesn't drag your estimate down.
Safety notes
Estimating from a submaximal set is safer than testing a true single-rep max, especially for beginners, lifters training alone, or anyone returning from injury. If you do decide to test a true 1RM, use a spotter or safety pins on barbell lifts, and never chase a max when your form is breaking down or you're training to exhaustion elsewhere in the session.