How to use the One Rep Max Calculator (1RM)
- Enter the weight you lifted, in kilograms or pounds. The result is in the same unit.
- Enter how many repetitions you completed with good form.
- Read the average estimate and each formula.
- Use the percentage rows to plan training weights.
Formula used
Epley: weight × (1 + reps ÷ 30). Brzycki: weight × 36 ÷ (37 − reps). Lombardi: weight × reps^0.10. The estimate shown is the average of the three.
Worked example
Here is the One Rep Max Calculator (1RM) worked through with the example values shown above, so you can check each step by hand.
| Inputs | |
|---|---|
| Weight lifted | 100 |
| Repetitions completed | 5 |
| Result | |
| Estimated 1RM (average of three formulas) | 115.54285 |
| Epley | 116.66667 |
| Brzycki | 112.5 |
| Lombardi | 117.46189 |
| 90% of 1RM | 103.98857 |
| 80% of 1RM | 92.434283 |
| 70% of 1RM | 80.879998 |
| 60% of 1RM | 69.325712 |
Estimated 1RM by reps completed
For the default weight of 100.
| Repetitions completed | Estimated 1RM (average of three formulas) |
|---|---|
| 1 | 100 |
| 3 | 109.16489 |
| 5 | 115.54285 |
| 8 | 124.63968 |
| 10 | 130.85307 |
| 12 | 137.40296 |
The three formulas
Epley: 1RM = weight × (1 + reps ÷ 30). Brzycki: weight × 36 ÷ (37 − reps). Lombardi: weight × reps^0.10. For 100 lifted for 5 reps they give 116.7, 112.5 and 117.5, which average 115.5.
With one rep the estimate is just the weight lifted, 100. With ten reps the same weight implies a much higher max, an average of 130.9, though the formulas disagree more as reps go up.
How accurate is it
The estimates work best for sets of about 2 to 10 reps taken close to failure. Above 10 reps, endurance and technique matter more than strength and estimates become rough. Brzycki’s formula also breaks down as reps approach 37.
Treat the result as a planning number. Your true max can differ by several percent, and it varies from day to day and by exercise.
Training percentages
Programs often prescribe sets as a percentage of 1RM. Based on the 115.5 estimate, 90% is 104, 80% is 92.4, 70% is 80.9 and 60% is 69.3.
As a rough guide, heavy low-rep strength work uses 80 to 95%, moderate hypertrophy work 65 to 80%, and lighter work or warm-ups below that. Round to the plates you have.
Staying safe
Estimating a max from a submaximal set is safer than testing it, but the usual precautions still apply: warm up, use a spotter or safety bars for heavy lifts, and stop a set when form breaks down.
If you are new to lifting or returning from injury, build up gradually and consider advice from a qualified coach. This calculator provides an estimate and is not a training plan.
Frequently asked questions
What is a one rep max?
The heaviest weight you can lift once with correct form for a given exercise.
Which formula is best?
None is universally best. They agree closely for 3 to 8 reps, so the calculator shows the average of three.
How many reps should I use?
Between 2 and 10 gives the most reliable estimate. Sets of 1 return the weight itself and sets above 10 are less accurate.
Does it work in pounds and kilograms?
Yes. The result is in the unit you enter.
Is it the same for every exercise?
The formulas are the same, but your max differs by exercise, and the estimates are less reliable for isolation or machine movements.
Should I test my true max?
Only if you need to and with proper safety, such as a spotter. Many lifters use estimates from sets instead.
This calculator gives estimates for information only. Actual figures from a bank, employer, tax authority or doctor may differ. It is not financial, tax, legal or medical advice.