Health & Fitness
One Rep Max Calculator
Estimate your one rep max from any set, with training percentages for every rep count.
Result
Enter your numbers and press Calculate to see the result.
Calculating…
How a one rep max is estimated
Your one rep max is the heaviest weight you can lift once with good form. Rather than actually testing it — which is tiring and carries real injury risk — you can estimate it from a set you have already completed, because the relationship between load and reps is remarkably consistent.
| Formula | Equation | Character |
|---|---|---|
| Epley | 1RM = w × (1 + r ÷ 30) | The most widely used; slightly generous at high reps |
| Brzycki | 1RM = w × 36 ÷ (37 − r) | More conservative; breaks down past 10 reps |
| Lombardi | 1RM = w × r^0.10 | Holds up better at higher rep counts |
| O'Conner | 1RM = w × (1 + r ÷ 40) | The most conservative of the four |
Where w is the weight and r the reps completed. The calculator shows all four plus their average, because no single formula is right for everyone — and the spread between them tells you how much to trust the number.
Worked example
100 kg for 5 reps:
| Formula | Working | Estimate |
|---|---|---|
| Epley | 100 × (1 + 5/30) | 116.7 kg |
| Brzycki | 100 × 36/32 | 112.5 kg |
| Lombardi | 100 × 5^0.10 | 117.5 kg |
| O'Conner | 100 × (1 + 5/40) | 112.5 kg |
| Average | 114.8 kg |
A 5 kg spread across four formulas on a 115 kg max — about 4%. That is the honest precision of the method, and it is why chasing a single decimal place is pointless.
Training percentages
The practical value of knowing your max is that it sets every working weight in a programme:
| % of 1RM | Reps | What it trains |
|---|---|---|
| 100% | 1 | Maximal strength — testing, not training |
| 95% | 2 | Strength |
| 93% | 3 | Strength |
| 90% | 4 | Strength |
| 87% | 5 | Strength and power |
| 85% | 6 | Strength and power |
| 80% | 8 | Hypertrophy |
| 75% | 10 | Hypertrophy |
| 70% | 12 | Hypertrophy and endurance |
Most programmes are built on these percentages — 5×5 at 80%, 3×3 at 90%, and so on. Recalculate them when your max changes rather than adding weight by feel.
Accuracy: where the estimate holds and where it breaks
These formulas were fitted to sets of 1 to 10 reps and are most reliable in the 3–6 range. Outside that they drift:
- Above 10 reps the estimate becomes unreliable, because muscular endurance starts to dominate. Brzycki fails outright at 37 reps, where its denominator hits zero.
- The set must be near failure. Five reps with three left in the tank estimates a max that is substantially too low.
- Exercise matters. Squats and deadlifts involve large muscle groups and typically allow more reps at a given percentage than bench press does, so a single table over-generalises.
- Training history matters. Experienced lifters tend to do fewer reps at a given percentage than beginners, because they can express more of their strength in a single effort.
Testing a true max
If you do want to test rather than estimate, the sensible protocol is a gradual ramp: warm up thoroughly, then work up in singles with 3–5 minutes of rest between attempts, stopping at the first genuine failure or the first rep where form breaks down. Three or four attempts above 90% is the practical limit before fatigue makes the result meaningless.
Testing belongs at the end of a training block, not in the middle of one, and always with a spotter on bench press. For most people an estimated max updated regularly is more useful than a tested max obtained rarely.
Training loads are only one part of progress — for the energy side, use the calorie and TDEE calculator, and for body composition the body fat calculator. Converting between kilograms and pounds is handled by the weight converter.
One Rep Max Calculator — frequently asked questions
How do I calculate my one rep max?
From a set you have already done near failure. The Epley formula is weight x (1 + reps/30), so 100 kg for 5 reps estimates 116.7 kg. This calculator shows four formulas and their average.
How accurate is a one rep max estimate?
Within about 5% when the set was 3 to 6 reps taken close to failure. The four formulas typically disagree by 4 to 5%, which is a fair measure of the method's real precision.
What percentage of my max should I lift for 5 reps?
About 87%. The common table runs 95% for doubles, 93% for triples, 85% for six, 80% for eight, and 75% for ten.
Why do the formulas give different answers?
Each was fitted to different data. Brzycki and O'Conner are more conservative, Epley and Lombardi more generous at higher reps. Averaging them is usually the most sensible single number.
Can I estimate my max from a set of 15 reps?
Not reliably. These formulas were built for 1 to 10 reps, and beyond that muscular endurance dominates rather than strength. Brzycki fails completely at 37 reps, where its denominator reaches zero.