Least Common Denominator

What is a Denominator?

The denominator is the bottom number in a fraction.

It shows how many equal parts the item is divided into


The denominator of ½ is 2

Common Denominator?

When the denominators of 2 or more fractions are the same, they have Common Denominators.


¾ and ¼ have Common Denominators

Finding a Common Denominator

One simple answer is to multiply the current denominators together.


¾ and ½

One of common denominators of those fractions is

4 × 2 = 8

So instead of having 4 or 2, we will make both of them have 8.

They now have common denominators (but not the least common denominator)

Least Common Denominator

Least Common Denominator is the smallest of all the common denominators.

how to find out?

  1. List the multiples of denominators
  2. Find the smallest number that is the same


FractionMultipe of denominatorSmallest common multiple
¾4, 8, 12, 16, …4
½2, 4, 6, 8, …4

So the Least Common Denominator of ¾ and ½ is 4.

Learn More

Rationalize the Denominator

Mixed Fractions

Improper Fractions

Simplest Form of Fractions

Definitions Index