One Rep Max Calculator
Calculate your one-repetition maximum (1RM) using seven proven strength training formulas. Your 1RM is the maximum weight you can lift for a single repetition with proper form. This calculator is essential for powerlifting programming, progressive overload planning, and determining training percentages for hypertrophy, strength, and power development. See also our Bench Press Calculator and Body Fat Calculator.
How to Calculate Your One Rep Max
Calculating your one rep max does not require you to actually attempt a maximal lift, which can be dangerous without proper spotters and experience. Instead, you can estimate your 1RM using submaximal testing — performing a set with a lighter weight to failure or near-failure, then applying a mathematical formula. Here is how to do it step by step:
- Warm up thoroughly: Perform 2-3 warm-up sets with progressively heavier weights. Start with 50% of your estimated working weight and increase to about 70-80%.
- Choose a test weight: Select a weight you can lift for 3-10 repetitions. The fewer reps you use, the more accurate the estimate. Ideally, use a weight you can lift for 3-5 reps.
- Perform the set: Lift the weight with strict form until you reach technical failure (the point where your form begins to break down). Do not sacrifice form for extra reps.
- Record your numbers: Note the exact weight lifted and the number of complete repetitions performed with good form.
- Enter the values above: Input your weight and reps into this calculator to get your estimated 1RM from all seven formulas.
- Use the average: The average of all formulas provides the most reliable estimate. For rep ranges of 1-5, the Brzycki and Epley formulas tend to be most accurate.
One Rep Max Formulas
Seven validated formulas are used in exercise science to estimate one-repetition maximum. Each formula was developed through regression analysis of actual 1RM testing data. They differ slightly in their predictions, especially at higher rep ranges.
Epley (1985): 1RM = weight × (1 + reps / 30)
Brzycki (1993): 1RM = weight × (36 / (37 - reps))
Lander (1985): 1RM = (100 × weight) / (101.3 - 2.67123 × reps)
Lombardi (1989): 1RM = weight × reps^0.10
Mayhew et al. (1992): 1RM = (100 × weight) / (52.2 + 41.9 × e^(-0.055 × reps))
O'Conner et al. (1989): 1RM = weight × (1 + 0.025 × reps)
Wathen (1994): 1RM = (100 × weight) / (48.8 + 53.8 × e^(-0.075 × reps))
All formulas take two inputs: the weight lifted and the number of repetitions completed. The exponential formulas (Mayhew and Wathen) use Euler's number (e ≈ 2.71828) and tend to produce slightly different results at higher rep ranges compared to the linear formulas (Epley and O'Conner).
Example Calculation
Let's work through a complete example using 225 lbs for 5 repetitions — a common bench press working set for intermediate lifters:
Epley: 225 × (1 + 5/30) = 225 × 1.1667 = 262.5 lbs
Brzycki: 225 × (36 / (37 - 5)) = 225 × 1.125 = 253.1 lbs
Lander: (100 × 225) / (101.3 - 2.67123 × 5) = 22500 / 87.94 = 255.9 lbs
Lombardi: 225 × 5^0.10 = 225 × 1.1746 = 264.3 lbs
Mayhew: (100 × 225) / (52.2 + 41.9 × e^(-0.275)) = 22500 / 84.03 = 267.8 lbs
O'Conner: 225 × (1 + 0.025 × 5) = 225 × 1.125 = 253.1 lbs
Wathen: (100 × 225) / (48.8 + 53.8 × e^(-0.375)) = 22500 / 85.73 = 262.5 lbs
The estimates range from approximately 253 to 268 lbs, with an average of about 259.9 lbs. This means if you can bench press 225 lbs for 5 reps, your estimated one rep max is approximately 260 lbs. The variation between formulas is normal and expected — using the average provides the most balanced estimate.
1RM Percentage Chart
Once you know your 1RM, you can use percentage-based training to program your workouts. The following table shows the relationship between repetitions and the percentage of your one rep max. These percentages are based on research averages and may vary slightly between individuals and exercises.
| Reps | % of 1RM | Training Goal |
|---|---|---|
| 1 | 100% | Max Strength / Testing |
| 2 | 95% | Max Strength |
| 3 | 93% | Max Strength |
| 4 | 90% | Strength |
| 5 | 87% | Strength |
| 6 | 85% | Strength / Hypertrophy |
| 7 | 83% | Hypertrophy |
| 8 | 80% | Hypertrophy |
| 9 | 77% | Hypertrophy |
| 10 | 75% | Hypertrophy / Endurance |
| 11 | 73% | Muscular Endurance |
| 12 | 70% | Muscular Endurance |
Epley vs Brzycki Formula Comparison
The Epley and Brzycki formulas are the two most widely used 1RM prediction equations in strength training. Understanding their differences helps you choose the right one for your situation.
The Epley formula (1RM = weight × (1 + reps/30)) is a linear equation that tends to produce slightly higher estimates, especially at higher rep ranges (8-12 reps). It was developed in 1985 and is popular because of its simplicity. The Epley formula works well for compound movements like squats and deadlifts where experienced lifters can maintain form at higher rep ranges.
The Brzycki formula (1RM = weight × 36/(37 - reps)) produces more conservative estimates and is considered more accurate for rep ranges of 1-7. It was published in 1993 by Matt Brzycki and is widely used in academic research. The Brzycki formula is particularly reliable for upper body pressing movements like the bench press.
Which is more accurate? Research suggests that for low rep ranges (1-5 reps), both formulas produce similar and accurate results — typically within 5% of actual 1RM. For moderate rep ranges (6-10), the Brzycki formula tends to be slightly more accurate. For high rep ranges (10+), both formulas lose accuracy, but the Epley formula tends to overestimate more than Brzycki. For the most reliable estimate, use a weight you can lift for 3-5 reps and average the results from multiple formulas.
It is worth noting that individual variation plays a significant role. Factors like muscle fiber composition, training experience, exercise selection, and fatigue level all affect the accuracy of any prediction formula. Slow-twitch dominant individuals may find their actual 1RM is lower than predicted, while fast-twitch dominant lifters may exceed predictions.
How to Use Your 1RM for Training
Knowing your one rep max is valuable for programming effective training cycles. Here are the primary ways to apply your 1RM in practice:
- Percentage-based programming: Most strength programs prescribe weights as a percentage of 1RM. For example, a program might call for 5 sets of 3 reps at 85% of your 1RM. If your 1RM squat is 300 lbs, you would use 255 lbs.
- Progressive overload tracking: By retesting your estimated 1RM every 4-8 weeks, you can objectively measure strength gains. An increase in estimated 1RM confirms your program is working.
- Training zone selection: Use 85-100% of 1RM for maximal strength development (1-5 reps), 67-85% for hypertrophy (6-12 reps), and 50-67% for muscular endurance (12-20+ reps).
- Periodization planning: Structure training blocks around different percentages. A typical linear periodization might start at 70% for 4 weeks, progress to 80% for 3 weeks, then peak at 90-95% for 2 weeks.
- Autoregulation: If you cannot hit the prescribed reps at a given percentage, your true 1RM may have changed. Adjust your training max (typically set at 90% of actual 1RM) accordingly.
- Exercise selection: Compare your 1RM across different lifts to identify weaknesses. For example, your front squat should be approximately 85% of your back squat 1RM. Significant deviations suggest muscle imbalances.
- Competition preparation: Powerlifters use 1RM estimates to plan attempt selection. First attempt is typically 90-93% of 1RM, second attempt 95-98%, and third attempt 100-102%.
- Deload planning: During deload weeks, reduce to 50-60% of 1RM to allow recovery while maintaining movement patterns and neural adaptations.
Frequently Asked Questions
How accurate are 1RM calculators?
1RM calculators are most accurate when using rep ranges of 1-5, typically predicting within 5% of your actual one rep max. Accuracy decreases as rep count increases — predictions based on 10+ reps can be off by 10-15%. For the best accuracy, test with a weight you can lift for 3-5 reps with good form. Individual factors like training experience, muscle fiber type, and exercise selection also affect accuracy.
Should I test my actual 1RM?
Testing your actual 1RM is appropriate for experienced lifters (2+ years of consistent training) who have proper form, access to safety equipment (power rack, spotter), and a specific reason such as competition preparation. For most recreational lifters, estimated 1RM from submaximal testing is safer and sufficient for programming purposes. The risk of injury increases significantly during maximal attempts, especially for beginners.
How often should I retest my 1RM?
Retest your estimated 1RM every 4-8 weeks, or at the end of each training block. Beginners may see changes every 2-4 weeks due to rapid neurological adaptations. Intermediate lifters typically retest every 6-8 weeks. Advanced lifters may only see meaningful changes over 8-12 week cycles. Avoid testing too frequently, as it can interfere with training progression and increase injury risk.
What percentage of 1RM should I train at?
The optimal training percentage depends on your goal. For maximal strength, train at 85-95% of 1RM for 1-5 reps. For muscle hypertrophy, use 67-85% for 6-12 reps. For muscular endurance, use 50-67% for 12-20+ reps. Most programs use a training max (90% of true 1RM) rather than actual 1RM to account for daily fluctuations and ensure quality reps throughout a training cycle.
Why do different formulas give different results?
Each formula was developed using different populations, exercises, and statistical methods. The Epley formula uses a linear model, while Mayhew and Wathen use exponential curves. These mathematical differences become more pronounced at higher rep ranges. At low reps (1-5), most formulas converge to similar values. The variation between formulas actually provides useful information — if all formulas agree closely, you can be more confident in the estimate.
Is 1RM the same for all exercises?
No, your 1RM is specific to each exercise. You will have different one rep maxes for bench press, squat, deadlift, overhead press, and every other lift. Additionally, the accuracy of 1RM formulas varies by exercise. Compound movements (squat, bench, deadlift) tend to produce more accurate predictions than isolation exercises (bicep curls, leg extensions). Machine exercises may also yield different results than free weight equivalents due to different stability demands.