One Rep Max Calculator
Enter the weight you lifted and the number of reps to estimate your one-rep max. Compare results from 7 proven formulas and see a percentage chart for programming your training.
Formula Comparison
| Formula | Estimated 1RM | Difference |
|---|
Percentage Chart
| % | Weight | Typical Reps |
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Rep ranges are approximate guidelines based on common training programming. Individual performance may vary.
Free One Rep Max Calculator
Your one rep max (1RM) is the heaviest weight you can lift for a single repetition of a given exercise. It is the standard measure of absolute strength in powerlifting, weightlifting, and general strength training. Knowing your 1RM lets you program precise training loads, track progress over time, and compare strength across exercises and body weights.
How 1RM Formulas Work
Testing a true one rep max requires warming up to a single maximal effort, which can be taxing on the body and carries injury risk for less experienced lifters. Prediction formulas offer a safer alternative. You perform a set to near failure at a submaximal weight, record the weight and reps, and the formula estimates what your single-rep max would be. This calculator uses seven of the most validated formulas in exercise science:
- Epley — weight × (1 + reps / 30). One of the most widely used and researched formulas.
- Brzycki — weight × 36 / (37 − reps). Popular in strength training textbooks, very accurate for low rep ranges.
- Lander — (100 × weight) / (101.3 − 2.67123 × reps). A linear model that performs well across moderate rep ranges.
- Lombardi — weight × reps0.10. An exponential model that tends to produce conservative estimates.
- Mayhew — (100 × weight) / (52.2 + 41.9 × e−0.055 × reps). An exponential regression formula validated in college-age populations.
- O'Conner — weight × (1 + reps / 40). A simpler version of the Epley formula that produces slightly lower estimates.
- Wathen — (100 × weight) / (48.8 + 53.8 × e−0.075 × reps). An exponential model often used in collegiate strength programs.
By averaging all seven formulas, this calculator provides a more robust estimate than any single formula alone. The formula comparison table lets you see how each formula differs so you can choose the one that aligns best with your experience.
Using the Percentage Chart
Once you know your estimated 1RM, the percentage chart shows you what weight to use at different training intensities. Most structured strength programs prescribe loads as a percentage of your 1RM. For example, a powerlifting program might call for 5 sets of 3 reps at 85%, while a hypertrophy program might prescribe 4 sets of 10 at 70%. The chart provides the calculated weight for each percentage along with the typical rep range that percentage supports.
Tips for Accurate Estimates
For the most accurate prediction, use a weight that you can lift for 2 to 10 reps. All formulas lose accuracy at higher rep ranges (above 12) because muscular endurance becomes a larger factor. Perform your set with good form and stop when you cannot complete another rep with proper technique. Rest at least 3 to 5 minutes between heavy sets to ensure your muscles are fully recovered before your test set.
Frequently Asked Questions
What is a one rep max (1RM)?
A one rep max (1RM) is the maximum amount of weight you can lift for a single repetition of a given exercise with proper form. It is the gold standard for measuring absolute strength and is used by coaches and athletes to program training loads and track progress over time.
How is one rep max calculated?
One rep max is estimated using prediction formulas that take the weight you lifted and the number of reps you completed. The most common formulas are Epley (weight × (1 + reps / 30)) and Brzycki (weight × 36 / (37 − reps)). This calculator uses 7 proven formulas and averages them for the most accurate estimate.
Which 1RM formula is most accurate?
The Epley and Brzycki formulas are the most widely used and researched. They tend to be most accurate for rep ranges between 2 and 10. For higher rep ranges (above 10), accuracy decreases for all formulas. This calculator averages 7 formulas to give you the most reliable estimate possible.
How do I use a percentage chart for training?
A percentage chart shows what weight to use at different intensities relative to your 1RM. For example, 85% of your 1RM is typically used for sets of 5 reps, while 70% is used for sets of 10–12 reps. Coaches prescribe training loads as percentages so athletes can auto-regulate intensity based on their current strength level.
Is my data private?
Yes. This calculator runs entirely in your browser. Your weight and rep data are never sent to any server. There are no accounts, no tracking, and no data collection.