One Rep Max Calculator
How strong are you, really?
Enter a weight you’ve lifted and the number of reps you completed. We’ll estimate your one rep max (1RM). This is the maximum weight you could theoretically lift for one clean rep.
OFFSET Strength Calculator
Estimate your one rep max and training weights.
Please enter valid weight and reps values greater than zero.
Estimated 1RM
-
Training Max (90%)
-
-
-
-
3RM
-
5RM
-
8RM
-
10RM
-
| Percentage | Weight |
|---|---|
| 50% | - |
| 60% | - |
| 70% | - |
| 80% | - |
| 90% | - |
| 100% | - |
No calculations yet. Complete a calculation to see your history.
What is a one rep max?
Your one rep max, or 1RM, is the maximum weight you could lift for one repetition of an exercise with good technique.
It’s commonly used as a benchmark for strength and to calculate appropriate training loads.
But you don’t need to physically attempt your maximum to find it.
Our calculator estimates your 1RM from a weight and rep count you’ve already achieved, giving you a useful benchmark without having to load up the bar and hope for the best.
Why knowing your one rep max matters
Getting stronger is ultimately about creating a little more demand on your muscles over time.
More weight. More reps. Better control. More total work.
Knowing your estimated 1RM gives you a simple number to track as your strength improves.
If you lift 80kg for 8 reps today and, a few months later, manage 85kg for 8, your estimated 1RM makes that progress easy to see.
It can also help you choose the right weight when a programme asks you to train at a percentage of your maximum.
The problem with progressive overload
You know you need to add weight.
The problem is the machine doesn't always agree.
A cable stack might jump from 40kg straight to 45kg.
Your last set at 40kg is comfortable, but 45kg destroys your reps.
That’s a 12.5% jump in load just because the machine manufacturer decided that was your next option.
There is another way.
Make smaller jumps
The OFFSET Increment Pin lets you add smaller amounts of weight to compatible selectorised gym machines, helping bridge the gap between weight-stack increments.
Progress on your terms, not the stack's.
Frequently asked questions
How accurate is a one rep max calculator?
A 1RM calculator provides an estimate rather than an exact maximum. Accuracy varies depending on the exercise, number of reps performed, your training experience and how close the set was to failure.
For the most useful estimate, use a challenging set performed with good technique.
How many reps should I use to calculate my 1RM?
Lower-rep sets generally provide a better indication of your true one rep max. Sets of roughly 2–10 reps are usually most useful.
A 20-rep set can still produce an estimate, but there is considerably more room for individual differences in muscular endurance to affect the result.
Do I need to test my actual one rep max?
No. Unless max-strength testing is specifically important to your training, estimating your 1RM from a normal working set is often more practical.
You can then monitor whether your estimated maximum increases over time.
What percentage of my 1RM should I train at?
It depends on your goal and programme. Heavier percentages are typically used for lower-rep strength work, while lower percentages allow you to complete more repetitions and training volume.
There’s no single perfect percentage. Your 1RM is best used as a reference point rather than a rule.
Can I calculate my 1RM for gym machines?
Yes. The same principle can be useful for exercises such as leg extensions, leg curls, chest presses and cable exercises.
Just remember that machine weights aren't directly comparable between different machines or gyms. Track your progress on the same equipment where possible.