Question:** What is the greatest common factor of 72 and 108?

February 22, 2026

What Is the Greatest Common Factor of 72 and 108? A Clear Explanation

When working with numbers in math, one key concept students frequently encounter is the greatest common factor (GCF), also known as the greatest common divisor (GCD). If you’ve ever asked, “What is the greatest common factor of 72 and 108?”—you’re on the right track to mastering this essential concept. In this article, we’ll explore the GCF of 72 and 108 in detail, including step-by-step calculation methods and why understanding this number matters in math.

Understanding the Greatest Common Factor (GCF)

The greatest common factor of two or more integers is the largest positive integer that divides all of them without leaving a remainder. For example, the GCF of 72 and 108 is the largest number that evenly divides both 72 and 108.

How to Find the GCF of 72 and 108

There are three common methods to calculate the GCF:

Prime Factorization
Listing Factors
Using the Euclidean Algorithm

1. Prime Factorization Method

Break each number into its prime factors:

72 = 2³ × 3²
108 = 2² × 3³

Now, identify the lowest exponent of each common prime factor:

Common primes: 2 and 3
Smallest exponent of 2: 2¹ (or 2², taking the minimum of 2² and 2³ → 2²)
Smallest exponent of 3: 3²

Multiply these together: GCF = 2² × 3² = 4 × 9 = 36

2. Listing Factors (Suitable for Smaller Numbers)

List all factors of each number:

Factors of 72: 1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 36, 72
Factors of 108: 1, 2, 3, 4, 6, 9, 12, 18, 27, 36, 54, 108

The largest number appearing in both lists is 36.

3. Euclidean Algorithm (Efficient for Large Numbers)

The Euclidean algorithm uses repeated division. Here’s how it works:

Divide the larger number by the smaller: 108 ÷ 72 = 1 with remainder 36
Now divide 72 by 36: 72 ÷ 36 = 2 with remainder 0
When the remainder is 0, the last non-zero remainder is the GCF

So, GCF(72, 108) = 36

Why Is the GCF Important?

Understanding the GCF helps solve real math problems such as:

Simplifying fractions (e.g., GCF of numerator and denominator)
Reducing algebraic expressions
Solving word problems involving shared measurements or grouping items evenly
Finding common denominators when adding fractions

Final Answer

The greatest common factor of 72 and 108 is 36.

Knowing this number strengthens your foundation in number theory and prepares you for advanced math topics like ratios, proportions, and LCM (least common multiple) calculations. Whether you’re solving classroom problems or applying math in real life, mastering the GCF is a key skill.

Want to Practice More?

Try finding the GCF of other pairs—like 48 and 180—or explore how GCF relates to LCM in fractions and divisibility puzzles. With regular practice, identifying the greatest common factor becomes quick and intuitive.

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