One Rep Max Calculator – Estimate Your 1RM
Estimate your one-repetition maximum from a heavy set and get training percentages.
About the One Rep Max Calculator
What is the One Rep Max Calculator?
A one rep max calculator estimates the maximum weight you could lift once from a heavier multi-rep set.
Why use this calculator?
Knowing your 1RM lets you program percentage-based strength work without the risk and fatigue of actually testing a max.
How to use it
- Lift a weight for between 1 and 30 clean reps.
- Enter the weight and the number of reps.
- Read your estimated 1RM and the percentage table.
Formula
1RM ≈ weight × (1 + 0.0333 × reps).
Estimates drift with experience and fatigue. Avoid true max testing without a spotter.
Frequently Asked Questions
Is a real 1RM test better?
More accurate, but riskier. Estimated 1RMs match closely for practiced lifters and are safer for regular planning.
Can I use this for any lift?
Yes, though upper-body lifts tend to estimate slightly better than lower-body movements at high rep counts.
Is this a medical diagnosis?
No. This tool provides general wellness information only. It is not a substitute for evaluation by a qualified healthcare professional.
Why do results differ from my doctor's measurements?
Clinical measurements use calibrated equipment and professional technique. Home estimates rely on formulas and self-reported values, so small differences are normal.
How often should I recalculate?
Recheck after meaningful changes such as weight gain or loss, a new workout routine, or every few months to track trends over time.
Do these formulas apply to everyone?
Most population formulas are less accurate for athletes, pregnant people, very young children and the elderly. Use them as a general guide.
Is this calculator free to use?
Yes. Every calculator on this site is completely free, with no hidden fees, no subscriptions and no limits on how many times you can use it.
How accurate are the results?
We use standard, widely accepted formulas and calculate in your browser using double-precision arithmetic. Results are rounded for readability, so treat them as reliable estimates rather than a guarantee. Real-world factors can vary the true figure.
Can I add this calculator to my own website?
Yes. Open this calculator page and use the "Add to your website" box in the sidebar to copy a ready-made iframe snippet, then paste it into any HTML page.
Does it work on a phone or tablet?
Yes. The layout is fully responsive, so it works on desktops, laptops, tablets and mobile phones, and every input adapts to touch screens.