One-rep max calculator
Estimate your one-rep max from a set you've already done — and get the weight to use for any rep target. Plain maths, both standard formulas, shown honestly.
Most accurate for sets of about 3–10 reps.
Training weights from this max
| Reps | Weight | % of 1RM |
|---|
What a one-rep max is — and why estimate it
Your one-rep max (1RM) is the most weight you can lift for a single rep of an exercise. It's the reference point most strength programmes are built on: they prescribe work as a percentage of it — sets of 5 at 80%, say. But actually testing a true 1RM is taxing and a little risky, so most lifters never do. Estimating it from a normal working set gives you the same reference number without the max-effort grind.
How the estimate works
Enter a weight and the reps you managed with it, and the tool runs the two best-known formulas and averages them:
- Epley: 1RM = weight × (1 + reps ÷ 30)
- Brzycki: 1RM = weight × 36 ÷ (37 − reps)
Both are close for low-to-moderate reps and drift apart as the reps climb — which is the honest catch below.
Reps to a max: the percentage chart
The other direction is just as useful: given a max, what should you load for a target number of reps? These are the weights the calculator gives above, as round percentages of your 1RM.
| Reps | % of 1RM |
|---|---|
| 1 | 100% |
| 2 | 95% |
| 3 | 93% |
| 5 | 87% |
| 8 | 80% |
| 10 | 75% |
| 12 | 70% |
The honest caveats
An estimated 1RM is exactly that — an estimate. It's most reliable when your set is in the 3–10 rep range and taken close to failure; a weight you could have done ten more times tells the formula very little. Above about twelve reps the numbers get optimistic, and endurance starts to matter more than strength. Treat the figure as a training anchor, not a promise you'll hit on the platform.
Strength and running, on one plan
Knowing your numbers is step one. The harder part is fitting the lifting around your running so the two don't blunt each other — heavy legs and a hard run don't belong on back-to-back days. Here's how to train both, and why a bit of strength work makes you a more durable runner. It's also the whole idea behind Liftrun: it plans your runs and your lifts as one system, so a leg day never lands the day before a quality run. Want to know if your max is any good? See where it lands on the strength standards, or how your running and lifting stack up together on the hybrid fitness score.