Common Factor Calculator
Find all common factors shared between two or more numbers instantly — with step-by-step working shown.
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What is a Common Factor?
A common factor divides evenly into two or more numbers with no remainder. For example, 6 is a common factor of 12 and 18 because 12÷6=2 and 18÷6=3.
Step-by-Step Working
Every calculation shows complete working — all factors listed for each number, then the intersection to find all shared common factors.
3+ Numbers Supported
Enter as many numbers as you need separated by commas. Most tools only handle two — this calculator handles any amount.
Common Factor Calculator — Free Online Tool
A common factor (also called a common divisor) is any integer that divides exactly into two or more given numbers. Every pair of numbers shares at least 1 as a common factor. The largest of all common factors is called the Greatest Common Factor (GCF) or Highest Common Factor (HCF).
How to Find Common Factors
Step 1 — List all factors of each number (all integers that divide evenly into it).
Step 2 — Identify which factors appear in every list — these are the common factors.
Step 3 — The largest is the GCF.
Example: Factors of 12: 1, 2, 3, 4, 6, 12. Factors of 18: 1, 2, 3, 6, 9, 18. Common factors: 1, 2, 3, 6. GCF = 6.
Common Factors vs GCF
While the GCF Calculator gives only the single largest shared factor, this tool gives the complete list — useful for simplifying fractions, finding equivalent ratios, and understanding the full factor structure of your numbers.
Real-World Uses
Common factors are used to simplify fractions (divide numerator and denominator by a common factor), solve ratio problems, distribute items evenly into groups, and in algebra when factoring expressions. Related: LCM Calculator, Factor Calculator, Fraction Calculator.