Epley Formula Calculator

About Epley Formula Calculator

One-rep max (1RM) — the maximum weight you could lift for a single repetition — is a foundational reference number for strength training program design, since most structured lifting programs prescribe weights as a percentage of 1RM rather than an absolute number. Testing an actual 1RM directly carries injury risk and requires careful warm-up, which is why estimating it from a lighter, higher-rep set is the standard practical approach.

This tool uses the Epley formula, one of the most widely used 1RM estimation formulas: 1RM = weight × (1 + reps/30). It's derived from the observed relationship between how much weight can be lifted and how many reps that weight allows before failure — as reps increase, the percentage of true 1RM that weight represents decreases in a fairly predictable pattern.

The estimate is most accurate for sets in the lower rep range (roughly 10 reps or fewer) — the relationship between reps and percentage of 1RM becomes less reliable and more individually variable at higher rep counts, which is why very high-rep sets (15+ reps) produce a much less trustworthy 1RM estimate than a heavier, lower-rep set.

Alongside the estimated 1RM, the tool shows a percentage table (50% through 100%) — genuinely useful for programming, since many strength programs prescribe specific training weights as "80% of 1RM" or similar, and this table converts that percentage directly into an actual weight to load on the bar.

How it works

1. Enter the weight you lifted. For a set performed close to failure.
2. Enter the number of reps completed. Most accurate for 10 reps or fewer.
3. View your estimated 1RM and percentage table. Training weights at 50-100% of your estimated max.