# One-Rep Max Calculator

> Estimate your 1-rep max from any rep count using Epley or Brzycki formulas. See working weights at 50-90% of your max.

URL: https://uttir.com/one-rep-max-calculator
Categories: calculators
Privacy: All math runs locally. No data leaves your browser.

## About

Your one-rep max (1RM) is the heaviest weight you can lift for a single rep with good form. You rarely actually test it — going to true failure is fatiguing and risky. Instead, you do a set of 3-8 reps at a submaximal weight and use a formula to estimate what you could have done for 1 rep.

The two most common formulas are Epley (1RM = weight × (1 + reps/30)) and Brzycki (1RM = weight × 36 / (37 − reps)). Both work well in the 1-10 rep range; both overestimate above 10 reps. The tool defaults to the average of the two, which is the most accurate single estimate.

## How to use

1. **Enter a weight you actually lifted** — A set that challenged you but did not fail. Don't sandbag — use the real number.
2. **Enter the rep count** — How many clean reps you got. Stop counting at the first one that started to slow or shift form.
3. **Pick a formula** — Average is the most accurate. Epley tends to estimate slightly higher; Brzycki slightly lower.
4. **Read the working weights** — 50% / 60% / 70% / 80% / 90% of your estimated 1RM for warm-ups and working sets.

## Examples

### Bench press: 5 reps at 100 kg

Average of Epley and Brzycki formulas.

Output:

```
Estimated 1RM ≈ 112.5 kg; 80% = 90 kg; 90% = 101.3 kg
```

### Squat: 3 reps at 140 kg

Epley formula only.

Output:

```
Estimated 1RM ≈ 154 kg; 70% = 107.8 kg; 90% = 138.6 kg
```

## FAQ

### Are these formulas accurate?

Within ±5% for most lifters in the 1-10 rep range. The formulas assume you gave a true maximal effort on the test set, that your form was clean on every rep, and that the load is within your training range. They are estimates, not measurements. The only way to know your true 1RM is to test it — but the formulas are accurate enough for programming.

### Why do the formulas give different answers?

Epley assumes a linear drop in rep capacity. Brzycki assumes an inverse relationship that asymptotes as you approach 37 reps. In the 1-10 range they agree closely; above 10 reps they diverge. Epley tends to be slightly more optimistic at higher rep counts. Use the average of the two for a balanced estimate.

### How accurate above 10 reps?

Not very. Both formulas overestimate above 10 reps because the test set was so far from failure that the true 1RM is not predictable. If you can do more than 10 reps at a given weight, you should be training with heavier weight, not estimating a 1RM. Use a 1-5 rep test for the most accurate estimate.

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