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Greatest Common Factor Calculator

Please provide numbers separated by a comma "," and click the "Calculate" button to find the GCF.

Supports 2 or more whole integers (e.g. 48, 64, 80).
Quick Presets:

What is the Greatest Common Factor (GCF)?

In mathematics, the Greatest Common Factor (also known as the Greatest Common Divisor (GCD) or Highest Common Factor (HCF)) of two or more non-zero integers is the largest positive integer that divides all of them without leaving a remainder.

For example, consider 48 and 64:

  • Factors of 48: 1, 2, 3, 4, 6, 8, 12, 16, 24, 48
  • Factors of 64: 1, 2, 4, 8, 16, 32, 64

The common factors are 1, 2, 4, 8, and 16. The largest among them is 16, meaning GCF(48, 64) = 16.

3 Methods to Find the Greatest Common Factor

1. Prime Factorization

Standard

Break each number into prime powers. The GCF is the product of only the prime factors that are common to all numbers, raised to their lowest exponent:

GCF = ∏ pᵢ^(min eᵢ)

2. Euclidean Algorithm

Most Efficient

Repeatedly apply division modulo: gcd(a, b) = gcd(b, a mod b). The last non-zero remainder is the GCF:

a = q · b + r

3. Listing Divisors

Direct

List every positive divisor for each integer, determine their common intersection, and identify the highest element.

Practical Applications of the Greatest Common Factor

➗ Simplifying Fractions

Dividing both the numerator and denominator by their GCF reduces any fraction to its simplest irreducible form in one step (e.g. 48/64 ÷ 16/16 = 3/4).

📦 Grouping Without Leftovers

Distributing distinct quantities of items (e.g. 48 apples and 64 oranges) into identical gift bags with zero leftovers requires calculating the GCF.

📐 Tiling & Space Partitioning

Finding the largest square tile size that can tile a rectangular floor (e.g. 48m × 64m) without cutting any tiles uses the GCF.

Frequently Asked Questions

What does it mean if two numbers are coprime?

Two numbers are coprime (mutually prime or relatively prime) if their greatest common factor is 1 (e.g. GCF(15, 28) = 1). They share no common prime factors.

What is the GCF of a number and 0?

For any non-zero integer a, GCF(a, 0) = |a|, because every non-zero integer divides 0 without remainder (0 = 0 × a). However, GCF(0, 0) is undefined.

Are GCF, GCD, and HCF the same thing?

Yes. Greatest Common Factor (GCF), Greatest Common Divisor (GCD), and Highest Common Factor (HCF) are completely synonymous mathematical terms.