One Rep Max Calculator
This one rep max calculator estimates the heaviest weight you could lift once (your 1RM) from a set you took to failure, so you don’t have to test a true max. Enter the weight and the number of reps. You get the average of six well-known equations, each formula’s own estimate, how far they disagree and a chart of loads for 1 to 12 reps.
Updated
Results
- Epley
- Brzycki
- Lombardi
- O’Conner et al.
- Mayhew et al.
- Wathen
- Spread between formulasHighest minus lowest estimate
- ReliabilityShown when you enter more than 10 reps
| Reps | % of 1RM | Load |
|---|
Results are estimates. See the methodology below.
How to use the calculator
- Choose US (lb) or metric (kg) units.
- Enter the weight you lifted in a recent set.
- Enter how many full reps you completed with good form before you could not do another one. Use a whole number from 1 to 12.
- Read your estimated 1RM, the six individual estimates and the spread between the highest and lowest. A reliability note appears if you entered more than 10 reps.
- Use the table to see roughly what load matches a given number of reps.
The estimate only works if the set really went to (or very close to) failure. If you stopped with several reps left, the result will be too low.
Formulas used
With w = weight lifted and r = reps, the calculator applies six equations in the form compared by LeSuer and colleagues (Journal of Strength and Conditioning Research, 1997):
| Equation | Estimated 1RM |
|---|---|
| Epley (1985) | w × (1 + r/30) |
| Brzycki (1993) | w × 36 / (37 − r) |
| Lombardi (1989) | w × r^0.10 |
| O’Conner et al. (1989) | w × (1 + 0.025 × r) |
| Mayhew et al. (1992) | 100w / (52.2 + 41.9 × e^(−0.055r)) |
| Wathen (1994) | 100w / (48.8 + 53.8 × e^(−0.075r)) |
The headline result is the average of the six, because no single equation fits every lifter or exercise. With 1 rep, every formula returns the weight itself (taken literally, Epley, O’Conner, Mayhew and Wathen would give slightly more than you lifted).
The rep chart divides your estimated 1RM by the average factor for each rep count, so the row for your own reps shows exactly the weight you entered.
Not included: reps in reserve or RPE, exercise-specific equations, and adjustments for sex, age or training experience.
Examples
185 lb for 5 reps
The estimates are Epley 215.8 lb, Brzycki 208.1 lb, Lombardi 217.3 lb, O’Conner 208.1 lb, Mayhew 220.2 lb and Wathen 215.7 lb. The average is 214.2 lb, with a spread of 12.0 lb between the lowest and highest. From the chart, 3 reps match about 195.3 lb (91.2% of 1RM), 8 reps about 171.9 lb (80.2%) and 10 reps about 164.1 lb (76.6%).
100 lb for 10 reps
Epley and Brzycki agree at 133.3 lb, while Lombardi gives 125.9 lb, O’Conner 125.0 lb, Mayhew 130.9 lb and Wathen 134.7 lb. Average: 130.5 lb, spread 9.7 lb.
135 lb for 12 reps
The average is 184.3 lb, but the equations range from 173.1 lb (Lombardi) to 194.4 lb (Brzycki), a spread of 21.3 lb, and the calculator shows its reliability note. A heavier set of fewer reps would give a more trustworthy number.
How to read the result
Treat your estimated 1RM as a planning number, not a promise. Indirect estimates can be off by 10% or more from a tested max, and the spread shows how much the equations themselves disagree for your set. Sets of fewer than 10 reps tend to predict better, which is why the calculator flags 11 and 12 reps.
A tested max can come out lower or higher than predicted, depending on technique and how used you are to near-maximal loads. If you do test a true 1RM, warm up, use a spotter or safety bars, and stop if your form breaks down.
Frequently asked questions
What is a one rep max?
Your one-repetition maximum (1RM) is the most weight you can lift for a single complete repetition of an exercise with proper form. Many training programs set loads as a percentage of it.
Which 1RM formula is the most accurate?
None is best for everyone. Results depend on the lift, the number of reps and the person. That is why this calculator averages six equations and shows the spread, so you can see how uncertain the estimate is.
Why are Epley and Brzycki the same at 10 reps?
At exactly 10 reps the two equations give the same factor, 1.333. At fewer than 10 reps Epley is slightly higher, and above 10 Brzycki is higher: at 12 reps with 135 lb, Brzycki gives 194.4 lb and Epley 189.0 lb.
How many reps should I use for the best estimate?
Fewer reps generally predict better. In a study of women’s bench press, prediction equations were more accurate when fewer than 10 reps to fatigue were used. So a heavier set of fewer than 10 reps is usually a better input than a light, high-rep set.
Can I use it for any exercise?
You can enter any lift, but the calculator applies the same six equations to every exercise, with no exercise-specific adjustment. For machines, dumbbells or unusual movements, treat the result as a rough guide.
How often should I do strength training?
The CDC says adults need at least 2 days a week of muscle-strengthening activity that works all major muscle groups. A trainer or your doctor can help you plan safely if you are new to lifting or have a health condition.
Sources
- Wikipedia — One-repetition maximum (estimation formulas and their accuracy)
- Mayhew JL et al. — Accuracy of prediction equations for determining 1RM bench press in women before and after resistance training, J Strength Cond Res 2008;22(5):1570–1577
- CDC — Adult Activity: An Overview (Physical Activity Guidelines for Americans)
This calculator gives an estimate for training purposes only. Lifting near-maximal loads carries a risk of injury; use a spotter and check with a qualified professional if you have an injury or health condition.