Testing a true one-rep max takes a full session, carries some risk, and needs an athlete who is technically ready for a maximal attempt. For most training decisions you do not need it. A good estimate from a heavy set of a few reps is close enough, and you get one every time the athlete trains.
The Epley formula
The most widely used estimate is Epley’s:
e1RM = load × (1 + reps ÷ 30)
So 100 kg for 5 reps gives about 117 kg, and 140 kg for 3 reps gives 154 kg. Turned around, it also tells you what percentage of 1RM a given rep max corresponds to:
- 2 reps ≈ 94% of 1RM
- 3 reps ≈ 91%
- 4 reps ≈ 88%
- 5 reps ≈ 86%
- 10 reps ≈ 75%
Why 2–5 reps
Every formula is fitted to average lifters, and the further a set is from one rep, the more individual differences take over. Some athletes can do 15 reps at 70%; others manage 8. Sets of 2 to 5 reps are heavy enough that the estimate stays close to the real thing for most athletes and most lifts.
Getting a useful estimate
- Use sets taken close to failure (around RPE 9 or above). A set of 5 with three reps left in the tank underestimates the max.
- Use the same lift with the same technique standard every time. A paused squat and a touch-and-go squat are different lifts.
- Follow the trend, not one number. A single estimate is noisy; five weeks of estimates show a direction.
- Test a true 1RM when it actually matters: before a competition or at the end of a strength block.
PeakPlan calculates e1RM automatically from the heaviest completed set of 2 to 5 reps in each session, using the Epley formula, and charts it next to tested 1RMs on each athlete’s Performance tab.