# One Rep Max Calculator

> Estimate your one-repetition maximum from a weight and the reps you managed, using the Epley and Brzycki equations, with a table of training loads.

Category: Health & fitness · Applies to: Worldwide · Last updated: 2026-10-29
Interactive calculator: https://calculators.geekmidst.com/calculators/one-rep-max-calculator

Your one-rep max (1RM) is the heaviest weight you could lift once. Instead of testing it, estimate it from a set of up to 10 reps taken close to failure.

Also called: 1RM calculator, Max lift calculator.

## Inputs
- Weight lifted (default 100)
- Unit (options: kg, lb; default kg)
- Repetitions completed (unit reps; default 5)

## Results
- Estimated 1RM (average)
- Epley estimate
- Brzycki estimate
- Unit

## Formula

```
Epley: 1RM = w × (1 + r ÷ 30);  Brzycki: 1RM = w × 36 ÷ (37 − r);  shown: the average of the two (a single rep is taken as the 1RM).
```

Where:
- w: weight lifted
- r: repetitions completed with good form

## Worked example
1. Epley: 100 × (1 + 5 ÷ 30) = 116.7 kg.
2. Brzycki: 100 × 36 ÷ (37 − 5) = 112.5 kg.
3. Average: (116.7 + 112.5) ÷ 2 ≈ 114.6 kg.

**Result:** Five reps at 100 kg suggests a one-rep max of roughly 113–117 kg, about 114.6 kg on average.

## What the result means

Treat the estimate as a planning number, not a target to attempt. The table converts it into common training loads, for example 80–85% of 1RM for sets of about 5–6.

## Assumptions and limits
- The set was performed with consistent technique and taken close to muscular failure.
- The equations were developed mainly on trained adults performing barbell lifts.
- Accuracy falls as reps rise; above about 10 reps the equations can be off by 10% or more.
- Results vary by lift and by person: endurance-trained lifters often manage more reps at a given percentage than strength-trained lifters.

## Questions

### Which formula is more accurate?

Neither is consistently better. They agree exactly at 10 reps; below that, Epley gives slightly higher numbers. Averaging them is a reasonable middle estimate.

### Is it safe to test a true 1RM?

Maximal attempts carry injury risk, particularly without a spotter or coaching. An estimate from a 3–5 rep set avoids that risk for most training purposes.

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_This is a general screening estimate for adults, not medical advice or a diagnosis. Talk to a qualified health professional about your health._

Source: GM¹X CalcVerse — https://calculators.geekmidst.com/calculators/one-rep-max-calculator