Your one rep max, often written as 1RM, is the heaviest weight you can lift for a single good repetition. It drives many training decisions, from choosing working weights to tracking whether you are getting stronger.
Testing a true one rep max is not always practical or safe, especially without a coach nearby. This calculator estimates your 1RM from a lighter set instead. Enter the weight lifted and the reps completed, and it gives you two estimates plus a table of training loads. For related tools, see our health calculators hub.
One Rep Max Calculator
Enter the weight you lifted and how many reps you completed, and this calculator will estimate your one rep max using the Epley and Brzycki formulas.
Your estimated one rep max
Training loads based on the Epley 1RM
| Percentage of 1RM | Weight |
|---|
What Is the One Rep Max Calculator?
The one rep max calculator estimates the most weight you could lift for one repetition, based on a set you have already done. If you pressed 100 lb for 10 solid reps, it works out what that suggests for a single all-out lift.
Coaches use percentage-based training, where working weights are set as a share of your 1RM, such as sets at 75%. Knowing your estimated max makes those instructions easy to follow.
The estimate is only as good as the set behind it. A hard set taken close to failure, with good form, gives a far better estimate than an easy set stopped early.
How It Works and the Formulas
This calculator uses two well-known formulas and shows both results, so you can cross-check them. If the numbers are close, you can feel more confident. If they differ a lot, your true max probably sits between them.
The first is the Epley formula:
1RM = w × (1 + reps ÷ 30)
The second is the Brzycki formula:
1RM = w × 36 ÷ (37 − reps)
In both formulas, w is the weight you lifted, in pounds or kilograms, and reps is the number of repetitions completed with that weight. The result uses the same unit you entered. The percentage table is built from the Epley result.
There is one special case. If you completed exactly 1 rep, that weight is your one rep max, so the calculator returns the weight itself. The Epley formula would otherwise add about 3%, overstating a lift you have actually done.
How to Use the One Rep Max Calculator
- Pick a recent set where you lifted a weight for between 1 and 30 reps with good form.
- Enter the weight you lifted.
- Choose the unit, pounds (lb) or kilograms (kg).
- Enter the number of reps you completed.
- Click Calculate and read your Epley and Brzycki estimates.
- Use the percentage table to find working weights for your training.
- To try another set, change the numbers and calculate again, or click Reset to start over.
Sets of about 3 to 10 reps usually give the most useful estimates. High-rep sets depend more on endurance than strength, so the formulas become less reliable there, which is why this calculator stops at 30 reps.
Worked Example
Suppose you lifted 100 lb for 10 reps. Here is each formula at work.
Epley: 100 × (1 + 10 ÷ 30) = 100 × 1.3333 = 133.3 lb.
Brzycki: 100 × 36 ÷ (37 − 10) = 100 × 36 ÷ 27 = 133.3 lb.
Both formulas agree here, giving an estimated one rep max of about 133.3 lb, which is a reassuring sign.
From that Epley result, the calculator also works out training loads: 66.7 lb at 50%, 93.3 lb at 70%, 106.7 lb at 80%, and 120.0 lb at 90%. The next section shows the full table.
Training Loads as a Percentage of 1RM
The table shows training loads for the worked example above, based on an estimated 1RM of 133.3 lb. Every load is the Epley result multiplied by the percentage.
| Percentage of 1RM | Load (lb) |
|---|---|
| 50% | 66.7 |
| 55% | 73.3 |
| 60% | 80.0 |
| 65% | 86.7 |
| 70% | 93.3 |
| 75% | 100.0 |
| 80% | 106.7 |
| 85% | 113.3 |
| 90% | 120.0 |
| 95% | 126.7 |
| 100% | 133.3 |
Lighter percentages around 50 to 70% suit higher-rep work and technique practice. Loads around 75 to 85% suit moderate-rep strength work, and loads above 90% are for very low reps only.
Important Points and Assumptions
Both formulas assume your set was taken close to your limit. If you stopped with several reps in reserve, the calculator will underestimate your max, because it can only use the reps you actually completed.
They also assume consistent, good technique. Results vary between exercises: an estimate from a squat does not transfer exactly to a bench press, and machines behave differently from free weights.
Estimates get less accurate as reps rise. The Brzycki formula is not defined at 37 reps and is unreliable well before that, so this calculator accepts 1 to 30 reps only.
Planning training and nutrition together? Our TDEE calculator for total daily energy expenditure and BMR calculator for resting metabolic rate can help set the calorie side.
Common Mistakes
The most common mistake is entering a set that was not hard. If you could have done five more reps, the estimate will come out far below your real max. Use a recent hard set instead.
Another mistake is mixing up units. If you lifted kilograms but select pounds, every result will be wrong. Always check the unit matches the plates you actually lifted.
People also treat the estimate as an exact promise. It is a guide, not a guarantee you can lift that weight today. Sleep, fatigue, and technique all affect performance.
Finally, avoid testing the full 100% load just to check the calculator. Work up gradually through the percentages instead.
How to Interpret Your Results
If the Epley and Brzycki results are within a few pounds or kilos, treat that range as your estimated max and pick working weights from the table. If they differ widely, be conservative and use the lower number.
Use the table to match the load to the goal of the session. Heavier percentages are for low-rep strength work, while lighter percentages allow more reps and more total work.
Retest with a fresh hard set every few weeks rather than testing a true single. If the estimate rises, your training is working. Our advanced calorie calculator for detailed calorie planning pairs well with this tool.
Frequently Asked Questions
What is a one rep max?
Your one rep max (1RM) is the heaviest weight you can lift for one repetition with good form on an exercise.
Which formula is more accurate, Epley or Brzycki?
Neither is exact for everyone. They often agree closely on sets around 10 reps and can drift apart on very low or high rep sets. Showing both lets you cross-check.
How many reps should my set have?
Sets of about 3 to 10 reps usually give the most reliable estimates. This calculator accepts 1 to 30 reps, but high-rep estimates are less dependable.
What if I did exactly one rep?
Then that weight is your one rep max. The calculator returns it directly instead of applying a formula, which would overstate it.
Can I use kilograms instead of pounds?
Yes. Choose kg in the unit menu. The formulas work the same way, and every result is shown in kilograms.
Should I try to lift my estimated 1RM?
Only with preparation, a warm-up, good form, and a spotter or safety setup. Many lifters never test a true single and train entirely from percentages of the estimate.
References
For strength training guidance, see the National Strength and Conditioning Association (NSCA).
Disclaimer: This calculator gives estimates only. An estimate is not a substitute for a properly supervised true 1RM test, and it is not medical advice. Always warm up before heavy lifting, use a spotter or safety equipment for near-maximal attempts, and stop if your form breaks down or you feel pain. Talk to a qualified coach or health professional if you are new to lifting or returning from injury.