# One-rep max calculator

> One-rep max (1RM) from a set of reps with the Epley, Brzycki, Lombardi and O'Conner equations, plus training loads from 50 % to 100 %.

Interactive version: https://www.calcopenly.com/health/one-rep-max-calculator
Subject: Health and fitness calculators

A one-rep max (1RM) is the heaviest load you can lift once with good form. It is estimated here from a set taken to failure with four equations: Epley, weight × (1 + reps ÷ 30); Brzycki, weight × 36 ÷ (37 − reps); Lombardi, weight × reps^0.10; and O'Conner, weight × (1 + 0.025 × reps). The main result is their mean, shown in kilograms and pounds.

Lifters use it to set training loads without a maximal attempt. With the default 100 kg for 5 reps, the four equations give 112.5 to 117.5 kg and a mean of 114.8 kg; the table then lists loads from 50 % to 100 % of that, with the reps Epley predicts at each.

The equations were fitted to groups of lifters and lose accuracy as reps rise, especially past 10. They are lift-specific, so an estimate from the bench press says nothing about the squat.

## Inputs

- **Weight lifted**
- **Reps completed**: Clean reps to failure in one set

## Results

- Estimated one-rep max (mean of four) (kg) — main result
- Estimated one-rep max in pounds (lb)
- Epley (kg)
- Brzycki (kg)
- Lombardi (kg)
- O'Conner (kg)

## Formula

$$
\text{Epley } w\left(1 + \tfrac{r}{30}\right) \quad \text{Brzycki } w\,\tfrac{36}{37 - r} \quad \text{Lombardi } w\,r^{0.10} \quad \text{O'Conner } w(1 + 0.025r)
$$

## Worked examples

### 100 kg for 5 reps

- Weight lifted: 100 kg
- Reps completed: 5
- **Epley: 116.7 kg**
- **Brzycki: 112.5 kg**
- **Lombardi: 117.5 kg**
- **O'Conner: 112.5 kg**
- **Estimated one-rep max (mean of four): 114.8 kg**
- Checked against: Python 3.8 decimal/math: 100(1 + 5/30), 100·36/32, 100·5^0.1, 100(1 + 0.125); mean of the four

### 225 lb for 10 reps

- Weight lifted: 225 lb
- Reps completed: 10
- **Epley: 136.1 kg**
- **Lombardi: 128.5 kg**
- **Estimated one-rep max (mean of four): 132.1 kg**
- **Estimated one-rep max in pounds: 291.1 lb**
- Checked against: Python 3.8 decimal: 225 lb = 102.0582833 kg; Epley 300 lb = 136.0777 kg; Lombardi 225·10^0.1 lb; mean 291.127 lb

### A single rep is already a 1RM

- Weight lifted: 140 kg
- Reps completed: 1
- **Estimated one-rep max (mean of four): 140.0 kg**
- **Epley: 140.0 kg**
- **O'Conner: 140.0 kg**
- Checked against: Convention stated in the steps: r = 1 returns the lifted weight for every equation (Brzycki and Lombardi give it exactly)

### 60 kg for 12 reps

- Weight lifted: 60 kg
- Reps completed: 12
- **Epley: 84.0 kg**
- **Brzycki: 86.4 kg**
- **Lombardi: 76.9 kg**
- **O'Conner: 78.0 kg**
- **Estimated one-rep max (mean of four): 81.3 kg**
- Checked against: Python 3.8 decimal/math: 60·1.4, 60·36/25, 60·12^0.1, 60·1.3; mean 81.3313

## Questions

### How do you calculate your one-rep max?

Lift a weight for as many clean reps as possible in one set, then apply an equation. Epley's is weight × (1 + reps ÷ 30), so 100 kg for 5 reps gives 116.7 kg; Brzycki's is weight × 36 ÷ (37 − reps), giving 112.5 kg. This calculator averages Epley, Brzycki, Lombardi and O'Conner, which gives 114.8 kg for that set.

### Which one-rep max formula is most accurate?

None is best for every lift or lifter, and they agree most at low reps. For 100 kg lifted 5 times the four span 112.5 to 117.5 kg, a 5 kg spread; for 60 kg lifted 12 times they span 76.9 to 86.4 kg, almost 10 kg. Estimates from sets of 10 reps or fewer are therefore more consistent, and the mean used here sits between the highest and lowest equation.

### How many reps can you do at 80 % of your one-rep max?

About 8, by the Epley equation solved for reps: 30 × (100 ÷ 80 − 1) = 7.5, rounded to 8. The table under the result lists loads and Epley rep estimates from 50 % to 100 %: at 90 % it gives 3 reps and at 70 % it gives 13. Real rep counts at a given percentage vary between lifts and between lifters.

### How accurate is the one-rep max calculator?

Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 4 worked examples whose answers come from independent sources; for example, “100 kg for 5 reps” is checked against Python 3.8 decimal/math: 100(1 + 5/30), 100·36/32, 100·5^0.1, 100(1 + 0.125); mean of the four.

### Where does the method come from?

LeSuer DA, McCormick JH, Mayhew JL, Wasserstein RL, Arnold MD. The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift. J Strength Cond Res 1997;11(4):211–213; Brzycki M. Strength testing — predicting a one-rep max from reps-to-fatigue. J Phys Educ Recreat Dance 1993;64(1):88–90; Epley B. Poundage chart. Boyd Epley Workout. Lincoln, NE: Body Enterprises; 1985.

## Sources

- LeSuer DA, McCormick JH, Mayhew JL, Wasserstein RL, Arnold MD. The accuracy of prediction equations for estimating 1-RM performance in the bench press, squat, and deadlift. J Strength Cond Res 1997;11(4):211–213
- [Brzycki M. Strength testing — predicting a one-rep max from reps-to-fatigue. J Phys Educ Recreat Dance 1993;64(1):88–90](https://doi.org/10.1080/07303084.1993.10606684)
- Epley B. Poundage chart. Boyd Epley Workout. Lincoln, NE: Body Enterprises; 1985