What is a One Rep Max (1RM)?
Your one rep max (1RM) is the maximum amount of weight you can lift for a single repetition of a given exercise with proper form. It is one of the most useful metrics in strength training because it gives you an objective measure of your absolute strength.
Track progress
Comparing estimated 1RMs over time shows whether you are getting stronger, even when rep ranges change.
Program your training
Many programs use percentages of your 1RM to set working weights for each session.
How to calculate 1RM
The safest way to estimate your 1RM is to perform a set to near-failure with a weight you can handle for 3–10 reps, then plug the result into a formula. Testing an actual 1RM is demanding and carries a higher injury risk, so estimation is preferred for most lifters.
Epley formula
The Epley formula is one of the most widely used 1RM estimators. It is simple and surprisingly accurate for most lifters:
For example, if you squat 100 kg for 5 reps, your estimated 1RM is 100 × (1 + 5/30) = 116.7 kg.
Other popular formulas
- Brzycki: 1RM = weight / (1.0278 − 0.0278 × reps). Tends to be more conservative at higher rep ranges.
- Lombardi: 1RM = weight × reps0.10. Slightly more aggressive for higher reps.
- O'Conner et al.: 1RM = weight × (1 + reps / 40). A simpler linear alternative.
Accuracy tip
Formulas are most accurate when based on a set of 1–10 reps. Sets above 12 reps introduce more error because muscular endurance becomes a bigger factor than maximal strength.
Why knowing your 1RM matters
- Strength benchmarks: Compare your squat, bench, and deadlift 1RMs against bodyweight standards.
- Load selection: Programs like 5/3/1, Starting Strength, and percentage-based peaking blocks all depend on your 1RM.
- Fatigue management: Estimated 1RM from each workout helps you spot when accumulated fatigue is masking your true strength.
- Motivation: Watching your estimated 1RM climb over weeks is one of the most satisfying ways to visualize long-term progress.
Track your real lifts with Lift Diary
This calculator gives you a quick snapshot, but the best way to watch your 1RM trend over time is to log every workout. Lift Diary automatically calculates estimated one rep max from each set and shows your progress on the dashboard.