1RM Calculator
Estimate your one-rep max (1RM) from a submaximal set. Enter the weight you lifted and how many reps you completed.
| Formula | Estimated 1RM |
|---|---|
| Average | — |
Enter weight and reps above to see estimates.
Best accuracy is usually around 1-10 reps. High-rep estimates vary more.
Understanding 1RM Estimation
Your one-rep max (1RM) is the most weight you can lift for a single controlled repetition. It's the foundation of percentage-based programming — knowing your 1RM lets you set precise training weights ("work up to 80% of your squat max") rather than guessing load from session to session.
Why estimate instead of test?
A true 1RM attempt is taxing: it stresses tendons and connective tissue, requires near-perfect technique under maximal load, and demands 4–7 days for full recovery. Testing too frequently accumulates fatigue faster than training can. Estimation lets you extract the same information from a submaximal set you'd do anyway — no extra recovery cost, no spotter required, no ideal gym conditions needed.
The six formulas
Each formula was developed from a different population and optimized for a particular rep range:
- Epley — The most widely used. Reliable for 1–10 reps.
- Brzycki — Linear model; performs closely to Epley in the 1–6 rep range.
- Lombardi — Uses a power function; tends toward conservative (lower) estimates.
- Mayhew — Exponential model developed with field athletes; more accurate at 6–10 reps.
- O'Conner — Similar to Epley but more conservative at higher rep counts.
- Wathan — Exponential model; useful as a cross-check against Mayhew.
When the formulas agree closely, the estimate is reliable. When they diverge by more than 5–10%, your rep count was probably too high. Keep estimation sets in the 2–6 rep range for best results — all formulas lose accuracy above 10 reps.
Putting your e1RM to work
Use your estimated 1RM to set training weights: 70–80% for higher-rep volume work, 80–87% for strength sets of 3–5 reps, and 90%+ for heavy singles or competition prep. Update your estimate every 4–8 weeks as your strength improves.
See the Understanding Your One-Rep Max guide for a full breakdown of each formula and how to build percentage-based programming from your results.