How to Calculate Your One-Rep Max (1RM)
Learn how to estimate your one-rep max safely from a set you can actually perform, using the Epley and Brzycki formulas, plus when to trust the number and when not to.
Your one-rep max (1RM) is the most weight you can lift for a single repetition of an exercise. It is the standard unit for measuring strength, setting training percentages, and comparing yourself against strength standards. The problem: actually testing a true 1RM is fatiguing and, for many lifters, risky. The solution is to estimate it from a submaximal set.
The idea behind 1RM estimation
There is a predictable relationship between how much you lift and how many reps you can do with it. If you can squat a weight for 5 clean reps, you can lift more than that for 1 rep. Estimation formulas turn a weight-and-reps pair into a projected single-rep maximum. They are most accurate in the 1–10 rep range and drift as reps climb higher.
The Epley formula
1RM = weight × (1 + reps ÷ 30)Example: 100 kg for 5 reps → 100 × (1 + 5/30) = 100 × 1.167 = 116.7 kg estimated 1RM. Epley is simple, popular, and tends to read slightly higher at high rep counts.
The Brzycki formula
1RM = weight × 36 ÷ (37 − reps)Example: 100 kg for 5 reps → 100 × 36 / (37 − 5) = 100 × 36 / 32 = 112.5 kg estimated 1RM. Brzycki is a touch more conservative than Epley at moderate reps, which many lifters prefer for programming.
Both formulas agree closely at low reps and diverge as reps increase. For the most reliable estimate, use a set of 3–6 reps taken close to (but not quite at) failure.
How to get an accurate estimate
- Warm up thoroughly so the working set is representative, not sandbagged.
- Pick a weight you can lift for 3–6 hard but technically clean reps.
- Stop 1–2 reps before form breaks down — grinding reps corrupt the estimate.
- Log the weight and reps and let the calculator project your 1RM.
- Retest every 4–8 weeks rather than every session; strength changes slowly.
When not to trust the number
- Very high rep sets (15+) push the formulas outside their accurate range.
- Grinding, form-breaking reps inflate the estimate.
- Highly technical lifts (like the snatch) depend on skill under fatigue, so estimates are shakier.
Used well, an estimated 1RM lets you program percentages, chase progress, and see your strength tier without ever risking a true max attempt. Log a solid set, let the math do the rest, and re-test on a schedule.
Put it into practice
GYMKA logs every set, estimates your 1-rep max, and shows your strength tier for each lift automatically. It is free to start.
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