Predicting your maximum strength
The One Rep Max (1RM) calculator estimates the heaviest weight you could lift for a single repetition, based on a weight and rep count you've already performed. Rather than testing your true maximum (which carries injury risk), you provide data from a submaximal set—say, 8 reps at 200 lbs—and the calculator projects what your single-rep limit likely is.
This estimate is useful for programming strength training, setting goals, and tracking progress over weeks or months without repeatedly maxing out.
The formula
1RM = weight × (36 / (37 − reps))
This is the Brzycki formula, one of the most widely used models in strength training. It works best for rep ranges between 1 and 10; beyond that, accuracy drops.
Worked example
Imagine you complete a set of 6 reps at 250 lbs on the barbell bench press.
Step 1: Plug the values into the formula.
- Weight = 250 lbs
- Reps = 6
Step 2: Calculate the denominator.
- 37 − 6 = 31
Step 3: Divide 36 by that result.
- 36 ÷ 31 = 1.161
Step 4: Multiply by the weight lifted.
- 250 × 1.161 = 290.3 lbs
Your estimated one rep max is approximately 290 lbs.
From this estimate, you can calculate training percentages. For instance:
- 80% of 290 = 232 lbs (strength work)
- 70% of 290 = 203 lbs (hypertrophy work)
- 60% of 290 = 174 lbs (endurance/volume work)
These percentages form the foundation of periodized training programs.
Training percentages at a glance
| Intensity | Purpose | Example (from 290 lbs 1RM) |
|---|---|---|
| 50–60% | Warm-up, technique | 145–174 lbs |
| 65–75% | Hypertrophy, volume | 189–218 lbs |
| 80–90% | Strength, power | 232–261 lbs |
| 90%+ | Testing, peaking | 261+ lbs |
Common mistakes to watch
Using reps beyond 10. The Brzycki formula assumes you're working in a range where neural and muscular factors align predictably. A set of 20 reps will produce an inflated 1RM estimate because fatigue and metabolic stress dominate at high reps, not pure strength.
Ignoring technique quality. The calculator assumes you performed reps with good form. If your last rep was a grind or involved excessive body English, the actual 1RM will be lower than predicted.
Treating estimates as absolutes. This is an estimate, not a guarantee. Your actual maximum might be 5–10% higher or lower depending on experience level, recovery, and individual variation. Use it as a guide for program design, not a ceiling.
Forgetting fatigue state. If you test your reps at the end of a long workout when you're already fatigued, your 1RM estimate will be conservative. For the most useful prediction, use a set performed early in your session when you're fresh.
Disclaimer: This calculator provides an estimate for training purposes only and is not a substitute for professional coaching or medical advice. Always prioritize proper form and listen to your body when training.