How to use the LCD calculator
Type 2 to 10 fractions separated by commas, such as 1/4, 5/6, 3/8, and press Find LCD. The calculator finds the least common denominator and rewrites each fraction over it.
What is the least common denominator?
The least common denominator (LCD) of some fractions is the smallest number that all their denominators divide into – the least common multiple of the denominators. Writing fractions over the LCD lets you add, subtract and compare them.
How to find the LCD
- List multiples of the biggest denominator until the others divide it: for 4, 6 and 8 – 8, 16, 24.
- Prime factors: take each prime with its highest power. 4 = 2², 6 = 2 × 3, 8 = 2³ → LCD = 2³ × 3 = 24.
\frac{1}{4} = \frac{6}{24} \qquad \frac{5}{6} = \frac{20}{24} \qquad \frac{3}{8} = \frac{9}{24}See also the LCM calculator for whole numbers and the fraction calculator, which uses the LCD to add and subtract.
Frequently asked questions
How do you find the least common denominator?
Find the least common multiple of the denominators – list multiples of the biggest one until the others divide it, or use prime factors.
What is the LCD of 1/4 and 1/6?
12: it is the smallest number both 4 and 6 divide into. 1/4 = 3/12 and 1/6 = 2/12.
Is the LCD the same as the LCM?
Yes – the LCD of fractions is the LCM of their denominators.
Do I have to use the least common denominator?
Any common denominator works (like multiplying the denominators), but the least one keeps the numbers small and means less simplifying.