You rarely need to actually attempt a true one-rep max — it is risky and unnecessary for most lifters. Instead you can estimate it from a normal set using a prediction formula. The two classics are Epley and Brzycki.
The answer first
Both formulas turn a multi-rep set into an estimated single-rep max:
Epley: 1RM = weight × (1 + reps / 30)
Brzycki: 1RM = weight × 36 / (37 − reps)Enter your set into the one-rep-max calculator and it shows both, plus a loading table. Use a set of 10 reps or fewer taken close to failure for the best estimate.
A worked example
Say you bench 100 kg for 5 clean reps:
| Formula | Calculation | Estimated 1RM |
|---|---|---|
| Epley | 100 × (1 + 5/30) | 116.7 kg |
| Brzycki | 100 × 36 / (37 − 5) | 112.5 kg |
The two are about 4 kg apart at 5 reps. At 2–3 reps they would be almost identical; at 10 reps the gap widens. Many lifters simply average the two, which the calculator also reports.
Why use fewer reps
The fewer reps in your test set, the smaller the extrapolation and the more accurate the estimate. A heavy triple predicts your max far better than a set of 15, because by 15 reps your performance is limited by muscular endurance and technique breakdown rather than pure strength. As a rule, trust estimates from 1–6 reps, treat 7–10 as decent, and ignore anything above ~12.
Turning 1RM into training weights
The point of knowing your max is choosing working weights. The standard percentage-of-1RM relationship looks like this:
| % of 1RM | Reps ≈ | Typical use |
|---|---|---|
| 100% | 1 | True max |
| 90% | 4 | Strength |
| 85% | 6 | Strength/hypertrophy |
| 80% | 8 | Hypertrophy |
| 75% | 10 | Hypertrophy/volume |
| 70% | 12 | Volume |
See the full % of 1RM reference table. From our 116.7 kg estimate, an 80% hypertrophy set would be about 93 kg for 8 reps.
Practical tips
- Test on a compound lift with good technique (squat, bench, deadlift, press).
- Use the same equipment and conditions each time so changes reflect strength, not setup.
- Re-estimate every few weeks rather than chasing daily numbers.
- Fuel the work — set your calories with the TDEE calculator and protein with the macro calculator.
Bottom line
Epley and Brzycki are both good; the difference between them is smaller than your day-to-day variation. Pick one (or average them), keep your test sets short, and use the result to program sensible training percentages.
This is general fitness information, not individualised coaching or medical advice.