About the One Rep Max Calculator
Your one rep max (1RM) is the heaviest weight you can lift for a single repetition with good form. Testing it directly is tiring and risky, so most lifters estimate it from a heavier set of a few reps.
This calculator shows the Epley, Brzycki and Lombardi estimates side by side and uses their average as the headline number. It then builds a percentage chart for 1–12 reps from the NSCA table, rounded to the nearest 5 lb (or 2.5 kg) so you can load the bar right away.
How to use
- Optionally pick the lift and choose pounds or kilograms (switching converts the weight you entered).
- Enter the weight and the number of clean reps you managed close to failure, e.g. 225 lb × 5.
- Read your estimated 1RM (the average) and compare the three formulas below it.
- Use the percentage chart and the training-zone table to choose weights for your next sessions.
One rep max formulas
| Formula | Equation | 225 lb × 5 |
|---|---|---|
| Epley (1985) | w × (1 + r ÷ 30) | 262.5 lb |
| Brzycki (1993) | w × 36 ÷ (37 − r) | 253.1 lb |
| Lombardi (1989) | w × r0.10 | 264.3 lb |
| Average | mean of the three | 260.0 lb |
w is the weight lifted and r the number of reps. If you did a single rep, that weight is your 1RM, so all three formulas return it unchanged (Epley is special-cased at r = 1).
Which formula should you trust?
Between 2 and 6 reps the three formulas agree within a few percent. As reps go up they drift apart: Brzycki becomes the most conservative, while Epley and Lombardi read higher. No single formula is right for everyone, which is why the headline here is the average.
- Sets of 3–6 reps give the most reliable estimates.
- Above 10 reps, muscular endurance dominates and errors grow quickly.
- Stick with the same method over time — the trend matters more than the exact number.
How to use the % chart and training zones
| Reps | 1 | 2 | 3 | 4 | 5 | 6 | 8 | 10 | 12 |
|---|---|---|---|---|---|---|---|---|---|
| % 1RM | 100 | 95 | 93 | 90 | 87 | 85 | 80 | 75 | 67 |
Percentages follow the NSCA chart. Typical zones: strength 85–100% for 1–5 reps, hypertrophy 67–85% for 6–12 reps, muscular endurance below 67% for 12+ reps. The chart shows the most you could do for that many reps, so for regular work sets leave one or two reps in the tank.
FAQ
Is a calculated 1RM accurate?
From a set of 3–6 reps it is usually within a few percent of a tested max. Accuracy drops above 10 reps and varies with experience, the lift and how close to failure you went.
Which number should I use – Epley, Brzycki or the average?
Use the average for programming. If you want to be conservative (for example when coming back from a break), use the Brzycki value, which is usually the lowest.
Can I use a set of 15 reps?
The calculator accepts up to 20 reps, but above 10–12 reps the estimate becomes unreliable. For a better number, add weight and retest with 3–8 reps.
Why are the chart weights rounded to 5 lb?
So you can load them with standard plates (2.5 lb on each side). Untick the rounding box to see exact values, or switch to kilograms to round to 2.5 kg.
Should I test my true max?
Only if you are experienced and have a spotter or safety bars. For most lifters an estimated max is enough to plan training and is far less risky.