What is a one-rep max?
Your one-rep max (1RM) is the heaviest weight you can lift for one repetition of an exercise. An estimated 1RM works backwards from a set you've already completed instead of requiring you to test your maximum directly.
For example, if you lift 100 kg for 5 reps, an estimated 1RM tells you how much you could theoretically lift for one rep based on that set. Your actual maximum can be higher or lower because rep performance varies between people and exercises.
How to calculate your one-rep max
This calculator uses the Epley formula for sets of two or more reps:
1RM = weight × (1 + reps ÷ 30) For 100 kg lifted for 5 reps: 100 × (1 + 5 ÷ 30) = 116.7 kg.
The same calculation works in pounds. For example, 100 lb for 5 reps gives an estimated 1RM of 116.7 lb. The unit changes the label, not the calculation.
If you're specifically estimating your maximum from a bench press set, try our Bench Press Calculator.
Why 1RM estimates vary
Several published formulas can estimate a one-rep max from the same set, and they do not always produce the same number. That's because the formulas use different mathematical relationships between weight and reps.
For practical use, consistency is more important than switching between formulas. If you use an estimated 1RM to track progress, using the same method each time makes changes in the estimate easier to interpret.
A single rep is already a one-rep max
If you enter one rep, there is nothing to estimate: the weight you actually lifted is already your one-rep max for that set.
The calculator therefore returns the weight unchanged when the input is 1 rep rather than applying a multi-rep formula that would increase it.
Training percentages of your 1RM
Once you have an estimated 1RM, you can express it as training percentages. For example, an estimated 1RM of 116.7 kg gives:
| Percentage | Weight |
|---|---|
| 100% | 116.7 kg |
| 95% | 110.8 kg |
| 90% | 105.0 kg |
| 85% | 99.2 kg |
| 80% | 93.3 kg |
| 75% | 87.5 kg |
| 70% | 81.7 kg |
| 65% | 75.8 kg |
| 60% | 70.0 kg |
The calculator works from the unrounded 1RM value when calculating these percentages, so rounding the displayed 1RM does not introduce additional rounding error into the table.
Estimated weight for other rep counts
You can also work backwards from an estimated 1RM to see the weight that corresponds to different rep counts using the same Epley model.
| Reps | % of 1RM | Weight |
|---|---|---|
| 1 rep | 100.0% | 116.7 kg |
| 2 reps | 93.8% | 109.4 kg |
| 3 reps | 90.9% | 106.1 kg |
| 5 reps | 85.7% | 100.0 kg |
| 8 reps | 78.9% | 92.1 kg |
| 10 reps | 75.0% | 87.5 kg |
| 12 reps | 71.4% | 83.3 kg |
These are model estimates rather than guaranteed rep limits. Actual performance varies by exercise, training experience, technique, and individual strength-endurance.
How accurate is an estimated 1RM?
A 1RM calculated from reps is an estimate, not a measurement. Lower-rep sets generally require less extrapolation, while higher-rep sets can be less reliable because endurance contributes more to the result.
- Rep count: lower-rep sets generally give the formulas less distance to extrapolate.
- Proximity to failure: if you had several reps left in reserve, the calculated 1RM may underestimate your actual maximum.
- Exercise: the relationship between reps and maximum strength differs between exercises.
- Individual differences: technique, experience and strength-endurance affect how many reps you can perform at a given percentage.
Why estimate your one-rep max?
Estimating your 1RM lets you track changes in strength without repeatedly testing a true maximum. For example, if the same 100 kg set produces an estimated 116.7 kg 1RM and a later set of 105 kg for 5 reps produces 122.5 kg, the estimated max has increased under the same calculation.
This makes an estimated 1RM useful as a consistent training reference, even though it should not be treated as an exact measurement of your maximum strength.
Frequently asked questions
How do I calculate my one-rep max?
For two or more reps, multiply the weight lifted by (1 + reps ÷ 30). For example, 100 kg for 5 reps gives 100 × (1 + 5 ÷ 30) = 116.7 kg using the Epley formula.
What is my 1RM if I only did one rep?
If you lifted a weight for one repetition, that weight is already your one-rep max for that set. The calculator returns it unchanged instead of applying a multi-rep formula.
How many reps should I use to estimate my 1RM?
Lower-rep sets generally give a more direct estimate because there is less extrapolation. Sets of a few reps taken close to failure are commonly useful for estimating a 1RM, while higher-rep sets can be less reliable.
Can I use the calculator in pounds?
Yes. Select lb and enter the weight in pounds. The same formula is used, so 100 lb for 5 reps gives an estimated 1RM of 116.7 lb.
Can I use this for squat, deadlift, and bench press?
Yes. The calculation uses only the weight and number of reps, so it can be used for different exercises. However, the relationship between reps and 1RM can vary between exercises, so an estimate from a lower-rep set is generally preferable to extrapolating from a high-rep set.