One Rep Max Calculator

by
Reviewed by: David Chen, CSCS

Certified Strength and Conditioning Specialist, committed to accurate fitness calculations and evidence-based training advice.

The **One Rep Max (1RM) Calculator** estimates the maximum weight you can lift for a single repetition of a given exercise. This tool uses various proven formulas, such as the Epley formula, to provide a highly accurate estimation based on the weight you can lift and the number of repetitions you completed. Use this to plan your training, track progress, and determine your strength levels without the risk of attempting a true 1RM.

One Rep Max (1RM) Calculator

(Reps should be between 1 and 15 for accurate estimation)

Estimated One Rep Max (1RM):

0.0

kg/lbs

One Rep Max Calculator Formula

The One Rep Max is an estimated figure, and several formulas exist. We primarily use the highly-regarded Epley formula, which is reliable for rep ranges up to 10-12 reps.

Epley Formula:

$$1RM = W \times (1 + \frac{R}{30})$$

Where W is the Weight lifted and R is the number of Reps.

Source 1: National Library of Medicine (Epley Validation) Source 2: Journal of Strength and Conditioning Research

Variables

  • Weight Lifted (W): The amount of weight (in your chosen unit, kg or lbs) you successfully lifted for multiple repetitions in a set.
  • Repetitions Performed (R): The total number of successful repetitions you completed with the weight W. The estimation is most accurate when R is between 2 and 12.
  • One Rep Max (1RM): The estimated maximum weight you can lift one time with proper form.

Related Calculators

Explore other tools to help optimize your training and fitness goals:

What is One Rep Max (1RM)?

The 1RM is a fundamental metric in strength sports and resistance training. It represents the gold standard for measuring absolute strength. Knowing your 1RM is crucial for structuring effective training cycles, as many popular training methodologies (like 5/3/1 or block periodization) prescribe working sets as a percentage of your 1RM. For example, a heavy set might be programmed at 85% of your 1RM.

While an actual 1RM attempt can be beneficial, it carries a high risk of injury and is taxing on the central nervous system. Estimation formulas provide a safer, less strenuous way to gauge strength levels, allowing athletes and casual lifters to continuously adjust their working weights based on their current performance without maxing out.

How to Calculate One Rep Max (Example)

Let’s look at an example using the Epley formula: A lifter performs 6 repetitions with 135 kg on the squat.

  1. Identify Variables: The Weight lifted (W) is 135 kg. The Repetitions Performed (R) is 6.
  2. Plug into Formula: $$1RM = 135 \times (1 + \frac{6}{30})$$
  3. Simplify Reps: $6 / 30 = 0.2$
  4. Calculate Multiplier: $1 + 0.2 = 1.2$
  5. Solve for 1RM: $1RM = 135 \times 1.2 = 162$
  6. Result: The estimated One Rep Max (1RM) is 162 kg.

Frequently Asked Questions (FAQ)

Is the estimated 1RM always accurate?

No. Estimation formulas provide a very close approximation, but accuracy depends on the rep range (2-12 is best), the specific exercise (more accurate for squats/bench press than isolation lifts), and the lifter’s technique and muscle fiber type distribution. Actual 1RM may vary by 2-5%.

What is the difference between the Epley and Brzycki formulas?

The Epley formula, used here, is simpler and tends to predict a slightly higher 1RM, often favored by powerlifters. The Brzycki formula uses a different constant in the denominator, $1RM = W \times 36 / (37 – R)$, and is also very popular. The results are usually close within the recommended rep range.

Why should I track my 1RM?

Tracking your 1RM is essential for progressive overload. It allows you to: 1) Measure progress over time, 2) Prescribe working weights (e.g., 70% of 1RM) accurately, and 3) Minimize the risk and fatigue associated with maximal lifting attempts.

What if I lifted 20 reps?

Formulas lose accuracy above 15 repetitions. Lifts above 15 reps are generally considered endurance rather than strength tests. The calculator will provide a result, but treat it as a rough estimate. For best accuracy, test with 3 to 8 reps.

V}

Leave a Comment