What this calculator does
A one rep max is the heaviest weight you can lift once with good form. Testing it directly is demanding and carries real injury risk, so most lifters estimate it from a set taken close to failure at a lighter weight.
Two formulas are shown. Epley and Brzycki agree closely at low repetitions and diverge as the set gets longer: which is why estimates from sets of ten or more should be treated with caution. Estimates from sets of three to six repetitions are considerably more reliable.
The formula
Both formulas fit the observed relationship between load and repetitions to failure. Epley scales linearly with repetitions; Brzycki uses a slightly different curve that reads lower at higher repetition counts. The average of the two is reported as the working estimate.
| Term | Meaning |
|---|---|
| 1RM | One repetition maximum: the heaviest single lift. |
| Epley | 1RM = weight × (1 + reps ÷ 30). |
| Brzycki | 1RM = weight × 36 ÷ (37 − reps). |
| Training percentages | Common working loads expressed as a share of 1RM. |
The inputs explained
| Field | What to enter |
|---|---|
| Weight lifted (kg) | The weight lifted, in kilograms. |
| Repetitions completed | Repetitions completed with good form. The estimate assumes the set was taken close to failure: stopping several reps short will understate the result. |
When to use it
Setting training loads
Most programmes prescribe percentages of 1RM. Estimating from a working set avoids the risk and fatigue of maximal testing while still giving usable numbers.
Tracking strength progress
Recalculate from a comparable set every few weeks. The estimated 1RM captures improvement even when the actual sets and repetitions stay the same.
Comparing lifts across rep ranges
A set of five at 100 kg and a set of ten at 85 kg are close in estimated maximum. Converting both to 1RM makes performances directly comparable.
Planning a peaking cycle
The 90 and 75 per cent figures correspond roughly to sets of three and ten. They are useful anchors for building a progression toward a genuine attempt.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
Estimated 1RM from an 80 kg set
80 kg lifted for varying numbers of repetitions.
| Repetitions | Estimated 1RM | Epley formula | Brzycki formula |
|---|---|---|---|
| 1 rep | 81.3 kg | 82.7 kg | 80.0 kg |
| 3 reps | 86.4 kg | 88.0 kg | 84.7 kg |
| 5 reps | 91.7 kg | 93.3 kg | 90.0 kg |
| 8 reps | 100.3 kg | 101.3 kg | 99.3 kg |
| 10 reps | 106.7 kg | 106.7 kg | 106.7 kg |
| 12 reps | 113.6 kg | 112.0 kg | 115.2 kg |
| 15 reps | 125.5 kg | 120.0 kg | 130.9 kg |
Training percentages at different loads
A set of five at different weights, with the working percentages that follow.
| Weight lifted | Estimated 1RM | 90% (3 reps) | 75% (10 reps) |
|---|---|---|---|
| 40 kg | 45.8 kg | 41.3 kg | 34.4 kg |
| 60 kg | 68.8 kg | 61.9 kg | 51.6 kg |
| 80 kg | 91.7 kg | 82.5 kg | 68.8 kg |
| 100 kg | 114.6 kg | 103.1 kg | 85.9 kg |
| 140 kg | 160.4 kg | 144.4 kg | 120.3 kg |
| 180 kg | 206.3 kg | 185.6 kg | 154.7 kg |
Questions
How accurate are 1RM estimates?
Good from sets of three to six repetitions, typically within a few per cent. Accuracy falls as the repetition count rises, because muscular endurance varies far more between individuals than maximal strength does.
Which formula should I use?
Either works at low repetitions. Brzycki reads lower at high repetition counts and is often considered more conservative there. The average of the two is shown as the working estimate.
Should I test my actual one rep max?
Only with proper preparation, good technique and ideally a spotter. Estimation is safer for most people, and for many training purposes just as useful. Novice lifters in particular are better served by building technique first.
Why does my estimate vary between sessions?
Sleep, nutrition, stress and accumulated fatigue all affect performance considerably. Use a rolling picture across several sessions rather than treating one estimate as definitive.
Does this work for every exercise?
It works best for compound barbell lifts: squat, bench press, deadlift, overhead press. Isolation exercises and machine work tend to allow more repetitions at a given percentage, so the formulas overestimate there.
For session energy cost, see calories burned. For protein to support training, use the macro calculator.