Fitness estimate, not a diagnosis
1-Rep Max (1RM) Calculator
Your one-rep max (1RM) is the most you could lift once. This tool estimates it from a set you actually did, then gives you the working weights for strength, muscle and endurance so you can train at the right load.
How to use this result
Treat the result as a general estimate, not a diagnosis or a personalised prescription. Its accuracy depends on the inputs and assumptions used by the tool. A trend over time is more useful than treating one number as a verdict.
You never need to test a true max to train smart. Do a solid set to near-failure, enter the weight and reps, and this gives your estimated 1RM plus practical training loads.
How the estimate works
- We use the Epley formula: 1RM = weight × (1 + reps ÷ 30).
- Strength work sits around 85–95% of 1RM.
- Muscle building sits around 67–80%; endurance below 67%.
Method and evidence
The tool uses the Epley equation: estimated 1RM = weight × (1 + repetitions ÷ 30). It is a programming estimate, not a measured maximum.
- Accuracy generally worsens as repetitions rise; a controlled set of roughly 3–8 reps is more useful than a high-rep set.
- Exercise, technique, fatigue and how close the set was to failure all affect the estimate.
Method updated: 2026-08-17
Frequently Asked Questions
How accurate is it?+
Very good up to about 5 reps; less accurate at high reps. Use a set of 3–8 reps for the best estimate.
Should I test my real 1RM?+
Rarely necessary and riskier solo. Estimating from a submaximal set is safer and accurate enough for programming.
Want to turn this estimate into a practical plan?
Share your result and main goal. We can explain a sensible next step for your current level.