1 Rep Max Calculator
Calculate your one-rep max for weightlifting exercises
How to Use
- Enter the weight you lifted for multiple reps
- Enter the number of reps you completed
- Select your preferred unit (kg or lbs)
- Choose a calculation formula (Epley is most common)
- Click calculate to see your estimated 1RM and training percentages
What is 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's a key metric in strength training used to measure progress, design training programs, and compare strength levels.
Testing your true 1RM can be physically demanding and carries injury risk. Instead, this calculator estimates your 1RM based on sub-maximal lifts, allowing you to safely predict your maximum strength potential.
1RM Calculation Formulas
Several formulas have been developed to estimate 1RM from sub-maximal lifts. Each has slight variations in accuracy depending on the rep range and exercise type:
- Epley Formula: Most commonly used, accurate for 1-10 reps. Formula: 1RM = weight × (1 + reps/30)
- Brzycki Formula: Popular alternative, most accurate for 1-12 reps. Formula: 1RM = weight × (36/(37-reps))
- Lander Formula: Good for moderate rep ranges (4-10 reps)
- Lombardi Formula: Uses exponential calculation, works across various rep ranges
- Mayhew Formula: Based on exponential decay, good for higher reps
- O'Conner Formula: Conservative estimate, similar to Epley but more conservative
- Wathan Formula: Another exponential formula, accurate for 1-20 reps
The Epley and Brzycki formulas are the most widely used and validated in research. For best results, test with a weight you can lift for 3-8 reps.
How to Test Your 1RM Safely
If you want to test your actual 1RM (not just estimate it), follow these safety guidelines:
- Warm up thoroughly with lighter weights and gradually increase
- Use a spotter for exercises like bench press and squats
- Rest 3-5 minutes between heavy attempts
- Use proper form - don't sacrifice technique for weight
- Make small jumps (2.5-5% increases) as you approach your max
- Stop if you feel pain (not just fatigue)
- Test 1RM no more than once every 4-6 weeks
- Consider testing on exercises like deadlift, bench press, and squat
Using Training Percentages
Once you know your 1RM, you can use percentage-based training to optimize your workouts for different goals:
| Percentage | Rep Range | Training Goal |
|---|---|---|
| 90-100% | 1-3 reps | Maximum strength and power |
| 80-90% | 3-6 reps | Strength development |
| 70-80% | 6-10 reps | Hypertrophy (muscle growth) |
| 60-70% | 10-15 reps | Muscular endurance |
| Below 60% | 15+ reps | Endurance and technique practice |
Most strength programs use percentages of your 1RM to prescribe training loads. This ensures progressive overload and appropriate intensity for your goals.
Limitations and Considerations
Keep these limitations in mind when using 1RM calculators:
- Estimates are most accurate when using 3-8 reps; accuracy decreases with higher reps
- Different formulas may give slightly different results (usually within 5-10%)
- Results vary by exercise - compound movements are more predictable than isolation exercises
- Beginners may get less accurate estimates due to technical limitations
- Fatigue, sleep, nutrition, and training experience all affect actual performance
- Always start conservatively when applying 1RM estimates to training
Frequently Asked Questions
- Which 1RM formula is most accurate?
- The Epley and Brzycki formulas are generally considered most accurate for 1-10 reps. Epley (1RM = weight × (1 + reps/30)) is the most commonly used. For best accuracy, test with a weight you can lift for 3-8 reps with good form.
- Can I test my actual 1RM instead of estimating it?
- Yes, but true 1RM testing should be done carefully with proper warm-up, spotters, and experience. For safety and practicality, many athletes and coaches prefer using estimated 1RM from sub-maximal lifts, especially for programming purposes.
- How often should I test or recalculate my 1RM?
- For programming purposes, recalculate your estimated 1RM every 4-6 weeks or when you notice significant strength changes. True 1RM tests should be performed less frequently (every 8-12 weeks) to avoid excessive fatigue and injury risk.
- Why do different formulas give different results?
- Each formula was developed from different research studies with different populations and rep ranges. Variations are usually small (5-10%) and all provide useful estimates. Use the same formula consistently for tracking progress over time.