# One-Rep Max Calculator

- **URL:** https://codeasystem.com/calculators/fitness/one-rep-max-calculator/
- **Category:** fitness
- **Description:** Estimate your one-repetition max from any set of 1–12 reps, with Epley as the primary formula and Brzycki for comparison.
- **Primary output:** Estimated one-rep max (Epley): 116.67 kg

## Inputs
- Weight lifted (name: `weight`, type: number, example: 100)
- Repetitions (name: `reps`, type: number, example: 5)

## Outputs
- Estimated one-rep max (Epley): 116.67 kg
- Brzycki formula: 112.5 kg
- 90% of estimated max: 105 kg

## Formula / methodology
```
Epley:   1RM = w × (1 + reps ÷ 30)
Brzycki: 1RM = w × 36 ÷ (37 − reps)
```

Both formulas extrapolate a submaximal set up to a theoretical single repetition. Epley’s linear model is the strength-training default; Brzycki’s hyperbolic version tracks it closely at low rep counts and diverges slightly toward twelve.

We cap input at 12 reps because beyond that the estimates balloon while real maximal-effort predictions collapse; fatigue and fiber-type differences dominate the math.

## Assumptions & limitations
- Set taken close to technical failure.
- Compound lifts (squat, bench, deadlift) fit the models best.
- Estimates; actual maxes vary by several percent with warm-up, sleep and adrenaline.

## How to use
1. **Log a hard set**; Use a weight you could lift between 1 and 12 times; 3 to 8 reps gives the most reliable extrapolation.
2. **Enter weight and reps**; Kilograms and whole repetitions; anything above 12 gets rejected as statistically unreliable.
3. **Program from percentages**; Strength blocks typically train at 80–90% of this number; the 90% row is pre-computed.

## Example
Five clean reps at 100 kg project to roughly a 116.67 kg one-rep max by Epley, with Brzycki agreeing near 112.5 kg; program percentages off the lower figure if unsure.

Result for these inputs:

```
Estimated one-rep max (Epley): 116.67 kg
```

## About this calculator
### Why not just test your true max?

Genuine one-rep attempts demand maximal neural readiness, ideal technique and a spotter; and they cost recovery. Submaximal testing every few weeks plus these formulas tracks progress with a fraction of the injury risk.

### Choosing between the formulas

Under six reps they differ by under two percent; many coaches simply take whichever estimate is lower for programming conservatism. The divergence beyond ten reps is exactly why input stops at twelve.

### Common percentage schemes

- 5×5 strength: ~80–85% of estimated 1RM.
- Hypertrophy: 65–75% for 8–12 reps.
- Speed/power work: 50–60%, moved fast.

## FAQs
### Which formula should I use?

Epley for general use; it is the de facto standard. Check Brzycki when rep counts climb past eight; if they diverge much, your set was probably not near failure.

### Does it work for isolation machines?

Loosely. Machine leverage varies wildly by brand, so treat those numbers as machine-specific personal benchmarks only.

### Why reject more than 12 reps?

Extrapolation error grows nonlinearly with rep count; beyond a dozen the formulas routinely overpredict by 10%+ versus tested maxes.

## Related calculators
- [Calories Burned Calculator](https://codeasystem.com/calculators/fitness/calories-burned-calculator/)
- [Target Heart Rate Calculator](https://codeasystem.com/calculators/fitness/target-heart-rate-calculator/)
- [Protein Intake Calculator](https://codeasystem.com/calculators/health/protein-intake-calculator/)
- [VO2 Max Calculator](https://codeasystem.com/calculators/fitness/vo2-max-calculator/)

---
Last updated: 2026-08-23 · Version: 1.0.0 · [HTML version](https://codeasystem.com/calculators/fitness/one-rep-max-calculator/)