Methodology
What this calculator actually estimates
An estimated one-repetition maximum (e1RM) converts a challenging multi-repetition set into a theoretical single-repetition load. It is useful for planning and trend tracking, but it is not a direct strength test.
This calculator runs the same set through seven established equations—Epley, Brzycki, Lander, Lombardi, Mayhew, O'Conner, and Wathan. It reports the median as the middle estimate and the lowest-to-highest result as the formula spread. That spread is not a statistical confidence interval; it only shows how much the equations disagree.
A primary comparison study found that equation accuracy varied by exercise, and research comparing 5-, 10-, and 20-repetition tests found the 5RM condition most predictive in the exercises studied. That is why a technically consistent, near-limit set of about 3–10 reps is usually more informative than a long endurance set.
Worked example: 225 lb for 5 reps
| Formula | Calculation | e1RM |
|---|---|---|
| Epley | 225 × (1 + 5 ÷ 30) | 262.5 lb |
| Brzycki | 225 × 36 ÷ (37 − 5) | 253.1 lb |
| Lombardi | 225 × 5^0.10 | 264.3 lb |
The equations do not produce one universally correct answer. Use the complete live comparison above, repeat the same method over time, and avoid treating a small estimated change as proof of a true strength change.
How to get a more useful estimate
- 1
Use a representative set
Choose a recent set performed with your normal technique and range of motion.
- 2
Record honest reps
Count only completed repetitions. A set stopped far from failure will understate the implied max.
- 3
Prefer lower rep counts
Equation error tends to increase as the test moves farther from one repetition.
- 4
Compare like with like
Track the same lift, equipment, technique, and formula summary over time.
