One Rep Max (1RM) Calculator Formula
Understand the math behind the one rep max (1rm) calculator. Each variable explained with a worked example.
Formulas Used
Estimated 1RM
estimated_1rm = round(one_rm)90% 1RM
ninety_pct = round(one_rm * 0.9)80% 1RM
eighty_pct = round(one_rm * 0.8)70% 1RM
seventy_pct = round(one_rm * 0.7)Variables
| Variable | Description | Default |
|---|---|---|
weight_lifted | Weight Lifted(lbs) | 185 |
reps_performed | Reps Performed | 5 |
one_rm | Derived value= weight_lifted * (1 + reps_performed / 30) | calculated |
How It Works
How One Rep Max Is Estimated
The Epley formula estimates the maximum weight you can lift for a single repetition.
Formula
1RM = Weight x (1 + Reps / 30)
This formula is most accurate for rep ranges of 2-10. For higher reps, accuracy decreases because muscular endurance becomes a larger factor.
Why 1RM Matters
Knowing your 1RM allows you to program training at specific percentages, ensuring appropriate intensity for strength, hypertrophy, or endurance goals.
Worked Example
You bench press 185 lbs for 5 reps.
weight_lifted = 185reps_performed = 5
- 011RM = 185 * (1 + 5/30)
- 021RM = 185 * 1.1667
- 031RM = 215.8, rounded to 216 lbs
- 0490% = 216 * 0.9 = 194 lbs
- 0580% = 216 * 0.8 = 173 lbs
Ready to run the numbers?
Open One Rep Max (1RM) Calculator