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1RM Strength Calculator
Free strength calculator: estimate a one-rep max from a 1–10 rep set using three formulas. The headline number is the median.
How the strength calculator estimates 1RM
Epley: weight × (1 + reps / 30). Brzycki: weight × 36 / (37 − reps). Lombardi: weight × reps^0.10. One rep equals the weight entered. The headline is the median. The range is the formula spread. Use 1–10 reps. RPE is shown as approximate RIR and does not rewrite the math.
How this is calculated
- These are named prediction equations, not a tested max.
- Plate rounding is 2.5 kg or 5 lb so the table matches a bar you can load.
For the limits of these equations, read how accurate 1RM calculators are.
Questions
What is a strength calculator?
A strength calculator estimates how much you could lift for one clean repetition from a set you already completed. ARC’s 1RM strength calculator is built for compound lifts such as bench, squat, and deadlift. Enter a 1–10 rep set; the headline is the median of three formulas.
What does 1RM mean?
One-rep max is the most weight you could lift for a single clean repetition. ARC estimates that from a set you already did, not from a tested max attempt.
How accurate are 1RM calculators?
They are prediction equations. The headline is the median of Epley, Brzycki, and Lombardi. The range is the spread between those formulas. Treat it as a planning number for loading, not a competition result. How accurate 1RM calculators are.
How many reps should I use to estimate 1RM?
Use 1–10 reps. One rep equals the weight you entered. Sets much above 10 are a poorer fit for these formulas. RPE is shown as approximate RIR and does not rewrite the math.
Why do different 1RM formulas give different results?
Epley, Brzycki, and Lombardi model the rep-max curve differently. ARC shows all three and uses the median so one optimistic equation does not become the only number you load.