About this 1 Rep Max
Testing a true 1 Rep Max (the heaviest weight you can lift once) places immense stress on the body and carries a risk of injury. This calculator estimates your 1RM based on a sub-maximal set (e.g., 5 reps), allowing you to plan training percentages safely.
Who this calculator is for
- Lifters who want an estimated one-rep max without testing a true max attempt.
- Strength athletes building percentage-based training plans.
- Coaches programming sets, reps, and working weights from recent performance.
When to use it
- Use this calculator after a hard set of reps to estimate max strength.
- Use it when setting percentage-based work for powerlifting or general strength training.
- Use it to compare progress across training blocks without maxing out weekly.
How to use this calculator
- Enter the Weight Lifted for a specific set.
- Enter the number of Reps Performed (ideally between 3-10 for accuracy).
- View your estimated 1 Rep Max and training percentages.
Key assumptions
- The estimate assumes the lift and rep count were performed with solid technique near true effort.
- Prediction formulas are most reliable in lower rep ranges and become less accurate as reps climb.
- A calculated 1RM is still an estimate and may differ from a real tested max on the platform or gym floor.
Accuracy and testing
Review formula sources, default test cases, assumptions, unit handling, rounding rules, and changelog for this calculator.
How this calculator works
Uses the Epley Formula: 1RM = Weight × (1 + Reps/30). This formula is widely used for compound lifts like Squats, Deadlifts, and Bench Press.
Inputs explained
Weight Lifted
The amount of weight on the bar during your test set.
Reps Performed
The number of complete repetitions you performed with good form.
Understanding your results
Use the 90% Training Max for programs like 5/3/1. Use the 75% (Hypertrophy) value for muscle-building sets (8-12 reps).
Example scenarios
Bench Press
Lifted 185 lbs for 5 reps. Est 1RM = 216 lbs.
Squat
Lifted 315 lbs for 3 reps. Est 1RM = 347 lbs.
Key Features
- Epley Formula
- Training Percentages
- Safe Estimation
Things to Keep in Mind
Less accurate for isolation exercises (curls, extensions) and for sets with very high reps (>10).
Tips & Best Practices
- Accuracy decreases as reps increase. A 1RM calculated from a 3-rep set is more accurate than one from a 15-rep set.
- Always use a spotter when testing actual heavy singles.
- Form matters more than weight. Don't count half-reps.
Glossary of Terms
- 1RM
- One Repetition Maximum. The maximum amount of weight one can lift in a single repetition.
- Training Max
- A conservative max (usually 90% of true 1RM) used to calculate weekly lifting weights to prevent burnout.