How to use this One rep max calculator
- Enter the total completed lift load in the selected units.
- Enter one to ten repetitions from the same completed set. Select Calculate.
- Compare the two estimates and the Epley percentage table; use the plate calculator to check which loads your inventory can make.
The formula and method
The lift estimate uses only your completed load and repetition count. Epley = load × (1 + reps ÷ 30); Brzycki = load × 36 ÷ (37 − reps). For a completed single repetition, this tool returns the actual load with both methods.
Use the same exercise, equipment, range of motion and repetition style when comparing sets. A machine-stack number and a free-weight barbell load describe different conditions.
The form accepts one to ten completed repetitions. The main result and percentage table use Epley; Brzycki appears as a comparison. Percentages from 50% to 90% are arithmetic fractions of the estimate, not a prediction of how many repetitions you can perform at each load.
Worked example
A completed 100 kg set for 5 reps gives Epley = 100 × (1 + 5 ÷ 30) = 116.67 kg and Brzycki = 100 × 36 ÷ (37 − 5) = 112.50 kg. The displayed 80% Epley load is 93.33 kg.
Understanding the estimate
- Both formulas are estimates, and their difference is not a confidence interval.
- Repetitions left in reserve, fatigue, equipment and technique affect how representative a set is.
- The result does not assess readiness or provide clearance to attempt a maximum.
Frequently asked questions
Why do Epley and Brzycki give different results?
They use different relationships between load and repetitions. The tool shows both so the model choice stays visible; it does not claim one is universally accurate.
Which estimate drives the percentage table?
Epley drives every percentage shown. For example, the 80% row is the Epley estimate multiplied by 0.80.
Can I compare different exercises with the same estimate?
The formulas use only load and reps. They do not normalize differences between exercises, machines or techniques.