Your one-rep max (1RM) is the greatest weight you can lift for a single repetition with proper form. Hevy estimates this value from the weight and reps you log, so you do not need to perform a maximum-weight lift to get an estimate.
This article explains how the calculation works, what the estimate means, and how to use it when planning your training.
How Does Hevy Calculate Your 1RM?
We estimate your 1RM from each set using a rep-to-percentage table. The number of reps you completed corresponds to a percentage of your estimated one-rep max. We then divide the weight you lifted by that percentage.
Estimated 1RM = weight lifted ÷ percentage for that rep count
When calculating this yourself, write the percentage as a decimal. For example, 75% becomes 0.75.
Example Calculation
If you lift 75 kg for 10 reps, the percentage used is 75%:
75 kg ÷ 0.75 = 100 kg estimated 1RM
This means the estimated one-rep max for that set is 100 kg. It does not mean you have lifted 100 kg or should attempt that weight.
The calculation works the same way in pounds. The result uses the same unit as the weight entered.
What Percentages Does Hevy Use?
Use the table below to find the percentage that corresponds to the number of reps you completed.
| Reps | Percentage used | Reps | Percentage used |
| 1 | 100% | 16 | 65% |
| 2 | 97% | 17 | 64% |
| 3 | 94% | 18 | 63% |
| 4 | 92% | 19 | 61% |
| 5 | 89% | 20 | 60% |
| 6 | 86% | 21 | 59% |
| 7 | 83% | 22 | 58% |
| 8 | 81% | 23 | 57% |
| 9 | 78% | 24 | 56% |
| 10 | 75% | 25 | 55% |
| 11 | 73% | 26 | 54% |
| 12 | 71% | 27 | 53% |
| 13 | 70% | 28 | 52% |
| 14 | 68% | 29 | 51% |
| 15 | 67% | 30 | 50% |
For anything above 30 reps, Hevy continues to use 50%. This means that, at the same weight, a set of 30 reps and a set of more than 30 reps will produce the same estimated 1RM.
For example, both 20 kg for 30 reps and 20 kg for 35 reps produce an estimate of 40 kg:
20 kg ÷ 0.50 = 40 kg estimated 1RM
What Can I Use My Estimated 1RM For?
An estimated 1RM can provide a starting point for training plans that use percentages to determine workout weights. The appropriate percentage depends on your training goals and individual ability.
For example, if your estimated 1RM is 100 kg and your training plan calls for 70% of your 1RM, the calculation is:
100 kg × 0.70 = 70 kg
This is an example of percentage-based planning, not a recommendation to use a particular weight or percentage.
How Accurate Is the Estimate?
Your estimated 1RM is a guide, not a confirmed maximum. The relationship between reps and weight varies between people and exercises, so a fixed percentage table cannot predict everyone’s strength exactly. NSCA
Estimates from higher-rep sets can also be less accurate than those from lower-rep sets. Treat these values with extra caution rather than assuming they represent a weight you can lift for one rep. PubMed
The table above explains how Hevy calculates the number. It is not a guarantee of how many reps you personally can complete at each percentage.
How to Use Your Estimate Safely
Do not treat the number shown in Hevy as an instruction to attempt a maximum-weight lift.
When choosing your training weights:
- Prioritize technique. Warm up and choose a weight you can lift with controlled, proper form.
- Increase gradually. Reduce the weight if you cannot maintain your form, and stop if an exercise causes pain.
- Ask for guidance. A qualified trainer can help you choose suitable weights and check your technique.
Common Questions
Why is my estimated 1RM higher than the weight I lifted?
For sets of two or more reps, the calculation divides your logged weight by a percentage below 100%. This produces an estimate higher than the weight used for that set.
For a one-rep set, the percentage is 100%, so the estimated 1RM equals the weight you logged. However, completing one rep at that weight does not necessarily mean it is the most you could lift.
Why does my estimate differ from another calculator?
Different estimation methods can produce different results. An estimated 1RM should not be treated as interchangeable with a directly tested maximum.
To reproduce Hevy’s calculation, use the rep percentages in this article rather than a different formula.
What should I check if my estimated 1RM looks incorrect?
Check that you logged the correct weight, number of reps, and weight unit for the set. Then use the percentage table above to check the calculation.
Remember to divide by the percentage as a decimal—for example, divide by 0.89 for five reps, not by 89.