The formula
The most common estimate is the Epley formula: e1RM = weight × (1 + reps ÷ 30).
Example: 100 kg × 8 reps → 100 × (1 + 8/30) = 126.7 kg. Do 102.5 × 8 two weeks later and your e1RM moved to 129.8 — you got stronger, no max attempt required.
Why estimate instead of test
True 1RM attempts are taxing, technically risky under fatigue, and tell you nothing new for training weights. An estimate from your normal working sets tracks the same trend while costing nothing extra.
e1RM also makes different rep ranges comparable: 5 reps at 90 kg and 10 reps at 77.5 kg land within a kilogram of the same estimate, so a program that alternates rep ranges still produces one clean strength line.
Accuracy limits worth knowing
Formulas are calibrated on sets of roughly 1–10 reps; beyond 10 the estimate inflates. Accuracy is best on big barbell lifts and worst on small isolation work. And the set has to be honestly hard — an RPE 6 set predicts little (see the RPE guide).
How seto uses e1RM
seto computes e1RM from every logged set and uses its trend to detect progress and plateaus per exercise — that trend is what drives the “what to lift today” suggestion for experienced lifters.