One Rep Max Calculator
Estimate your 1RM from any set
One Rep Max Calculator
One Rep Max (1RM): How the Estimate Works and How to Use It
What is a one rep max?
Your one rep max — written 1RM — is the heaviest weight you could lift for a single clean repetition of an exercise. It is the reference point almost every strength programme is written against: sets are prescribed as a percentage of it rather than as an absolute weight, so the same programme scales to any lifter.
Testing a true single is slow and carries real injury risk, so the number is normally estimated from a set you have already done. That is what this one rep max calculator does: enter the weight you lifted and how many reps you got, and it works backwards to the single you never had to attempt.
The formula
The answer above uses the Epley formula:
It treats each additional repetition as worth about 3.33% more weight. Six other published formulas — Brzycki, Lombardi, O'Conner, Wathan, Lander and Mayhew — are shown on every result page so you can see how much they disagree for your particular set.
How many reps should you use?
- 2–6 reps: the accurate zone. All the formulas cluster tightly here.
- 7–12 reps: usable, but the estimate starts to depend on which formula you pick.
- 13+ reps: you are measuring muscular endurance more than maximal strength — treat any number as a rough guide.
Whichever set you use, it should have been taken close to failure. A comfortable set of five understates your max exactly as much as it was easy.
Turning a 1RM into training weights
Once you have the number, load is usually prescribed as a percentage of it: roughly 85–95% for heavy strength work, 75–85% for the main working sets of most programmes, and 65–75% for volume, technique and speed work. Every result page prints that percentage table for your own max.
Pounds or kilograms?
Both. Every 1RM formula is a ratio, so the estimate comes out in whatever unit you entered — pick pounds or kilograms and the answer, the rep table and the training percentages all follow.
Common one rep max examples
See Also
- BMI Meaning - Check what given BMI means
- BMI Calculator (Imperial) - Body Mass Index Calculator (ft/in/lbs)
- BMI Calculator (Metric) - Body Mass Index Calculator (kg/cm)
- Ideal Weight Calculator (Imperial) - Find out the Ideal Weight for a given Height in feet/inches
- Ideal Weight Calculator (Metric) - Find out the Ideal Weight for a given Height in centimeters