How to calculate your 1RM without testing it
Your 1RM (one-rep max) is the heaviest load you can lift once on an exercise. Actually testing it is tiring and risky. You can estimate it from a normal set.
The principle
There is a fairly regular relationship between the load lifted and the number of reps you can do: the more reps, the lower the load as a percentage of your max. Estimation formulas use this relationship. They are reliable up to about 10 reps; beyond that, the error grows.
Epley formula
1RM ≈ weight × (1 + reps ÷ 30)
Example: 100 kg for 8 reps → 100 × (1 + 8/30) = 100 × 1.267 ≈ 127 kg.
Brzycki formula
1RM ≈ weight ÷ (1.0278 − 0.0278 × reps)
Example: 100 kg for 8 reps → 100 ÷ (1.0278 − 0.2224) = 100 ÷ 0.8054 ≈ 124 kg.
Both formulas give similar values. Epley tends to estimate slightly higher as the number of reps increases.
Quick table (% of 1RM by number of reps)
- 1 rep → 100%
- 2 reps → ~95%
- 3 reps → ~93%
- 5 reps → ~87%
- 8 reps → ~80%
- 10 reps → ~75%
- 12 reps → ~70%
What an estimated 1RM is for
- Tracking progress: the estimated 1RM smooths out "weight × reps" variations from one workout to the next and gives a clear strength curve per exercise.
- Managing intensity: programming sets at 70%, 80% or 85% of your 1RM becomes possible without ever doing a max test.
- Comparing different sets: 90 kg × 6 and 100 kg × 3 give an almost identical estimated 1RM — the second is not "better", just heavier.
An estimated 1RM remains an estimate: the true value depends on your technique, your tolerance for maximal effort and the exercise (it is more reliable on big compound lifts than on isolation work).
PrimeFeat calculates your estimated 1RM (Epley formula) on every loaded set, flags new records and draws your strength curve per exercise.