1RM Calculator
Enter a set you completed and this estimates the most you could lift once. Six formulas are shown, because they disagree — and the spread tells you how much to trust the number.
Your results
An estimate from a rep-max formula, not a tested max. Accuracy is best from sets of 3–6 reps and degrades sharply above 10, where individual differences in fatigue resistance dominate.
Why six formulas
Every 1RM formula is a curve fitted to a population, and they were fitted to different populations doing different lifts. Epley and Brzycki are the most widely used; Mayhew and Wathan were derived from bench press data; Lombardi uses a power function rather than a linear one.
At five reps they typically agree within a few kilograms. At twelve, the spread widens considerably — which is the honest signal that a 12-rep set is a poor basis for estimating a single.
The spread figure above is the gap between the highest and lowest estimate. A large spread means treat the number loosely.
How to use the estimate
- For programming percentages, an estimate is fine and much less fatiguing than testing a true max.
- Estimate from 3–6 reps where possible. That is the sweet spot for accuracy.
- Use a set taken close to failure. A set with four reps left in the tank will badly under-estimate.
- Re-estimate every few weeks rather than recalculating weekly.
- Do not chase the estimate. If it says 140 kg, that is not a licence to attempt 140 kg today.
Common questions
How accurate are 1RM calculators?
Reasonably accurate from sets of 3–6 reps — typically within a few percent. Above 10 reps they become unreliable, because tolerance for high-rep work varies a lot between people.
Which 1RM formula is best?
Brzycki tends to read lower and Epley higher. Averaging several is more robust than picking one.
Should I test my actual 1RM instead?
Rarely necessary unless you compete. Testing is fatiguing and carries more risk than estimating from a working set.
Why does the estimate differ between lifts?
Different lifts have different rep-strength relationships. Squats and deadlifts usually allow more reps at a given percentage than bench press.
Related calculators
Track the numbers, not just calculate them
MyFitsy stores your weight, measurements and every session, so the figures above become a trend instead of a one-off.
