Find every factor two numbers share, and see which shared factor is the greatest.

How to Use the Common Factor Calculator

Enter two positive whole numbers — the full list of shared factors and the greatest one among them both update as you type.

The site already runs a Greatest Common Factor Calculator, so it's worth being direct about what's different here. That one runs the Euclidean algorithm and hands back a single number — the GCF — with no visibility into how it got there. This one takes the slower, more visual route instead: it lists every factor of each number, intersects the two lists, and shows the whole set.

factors of 24: 1, 2, 3, 4, 6, 8, 12, 24
factors of 36: 1, 2, 3, 4, 6, 9, 12, 18, 36
common factors: 1, 2, 3, 4, 6, 12
greatest common factor: 12

Seeing 1, 2, 3, 4, 6, and 12 laid out together makes it obvious why 12 is the answer — it's simply the largest number on a list you can see in full, not a value handed down by an algorithm with no visible steps. That's the whole value of this calculator next to the GCF one: context over speed.

Every pair of numbers shares at least one common factor, 1, since 1 divides everything without exception. If 1 turns out to be the only entry on the list, the two numbers are coprime — no shared factor beyond the trivial one, even when neither number involved happens to be prime itself.