One Rep Max Calculator
Estimate your one-rep max (1RM) and view training percentage targets from 65% to 100% of your maximal weight lift.
Range: 1 – 36
What is a One-Rep Max (1RM)?
Your One-Rep Max (1RM) is the absolute maximum amount of weight you can lift for a single repetition of a specific exercise with proper technique. It is widely considered the ultimate benchmark of raw muscular strength.
Knowing your 1RM is essential for structural weight training. Instead of guessing how much weight to load onto a barbell, strength programs prescribe intensities as a percentage of your 1RM (e.g., 3 sets of 5 reps at 80% 1RM).
Direct Testing vs. Estimation
While you can test your 1RM directly by warming up and attempting single max effort lifts, this approach carries a high risk of injury, joint strain, and central nervous system fatigue.
Estimation calculators allow you to input a sub-maximal weight that you can lift for multiple repetitions (typically 2 to 10 reps) and apply mathematical formulas to predict your 1RM. This method is much safer and highly accurate for reps under 10.
The Scientific 1RM Formulas
There are several validated formulas used to estimate your 1RM. This calculator features the three most prominent:
1. Epley Formula (1885)
Developed by Boyd Epley, this is the most common equation used in athletic strength testing.
1RM = Weight × (1 + Reps / 30)
2. Brzycki Formula (1993)
Developed by Matt Brzycki, this equation is highly accurate for low reps (under 10) and is commonly used by powerlifters.
1RM = Weight / (1.0278 - (0.0278 × Reps))
3. Lander Formula (1985)
Developed by J. Lander, this formula predicts slightly different fatigue curves.
1RM = (100 × Weight) / (101.3 - (2.67123 × Reps))
% of 1RM Training Table
Strength training intensities target different adaptations based on percentages of your 1RM:
| % of 1RM Intensity | Average Reps Allowed | Primary Training Adaptation |
|---|---|---|
| **90–100%** | 1–3 reps | Absolute Maximal Strength |
| **80–89%** | 4–7 reps | Muscular Hypertrophy & Strength |
| **70–79%** | 8–12 reps | Muscular Hypertrophy (Muscle growth) |
| **60–69%** | 12–15 reps | Muscular Endurance & Hypertrophy |
| **< 60%** | 15+ reps | Local Muscular Endurance |
Guidelines for Estimation Testing
To get the most accurate 1RM estimate:
- Choose a weight you can lift for 3 to 8 repetitions before reaching muscular failure.
- Maintain strict form. If your form breaks down on the 5th rep, only count 4 completed repetitions.
- Perform the estimation when you are fresh and fully recovered.
Sources & Citations
- Brzycki M. Strength Testing—Predicting a One-Rep Max from Reps-to-Fatigue. Journal of Physical Education, Recreation & Dance. 1993.
- Epley B. Poundage Chart. Boyd Epley Enterprises. 1985.
- Lander J. Maximums based on reps. National Strength and Conditioning Association Journal. 1985;7:60-61.
Frequently Asked Questions
Your one-rep max (1RM) is the maximum amount of weight you can lift for a single repetition of an exercise with proper form. It is the gold standard for measuring raw muscular strength.
Testing your absolute 1RM places extreme stress on your muscles, joints, and nervous system, carrying a high risk of injury. Estimating it from a higher rep set (e.g., a 5-rep max) is much safer and highly accurate.
The Epley and Brzycki formulas are the most popular and yield very similar results for reps under 10. For reps over 10, calculations become less accurate because muscular endurance becomes the limiting factor rather than raw strength.
Workout programs often prescribe intensities as a percentage of your 1RM. For example, a strength phase might call for 5 reps at 85% of your 1RM. This table tells you exactly what weight matches that intensity.
1RM is most relevant for compound, multi-joint lifts like the bench press, back squat, deadlift, and overhead press. It is less useful and less safe for isolation exercises like bicep curls or leg extensions.