How this calculation works
Use the resulting denominator to rewrite the fractions before adding. For 6, 8 and 9, the scaling factors are 12, 9 and 8.
THE FORMULA
LCD = lcm(lcm(b,d),f)A worked example
The smallest common multiple of 6, 8, and 9 is 72.
Good to know
Reduce your fractions first if you want the smallest denominator of their reduced forms.
Reference: OpenStax Prealgebra (opens in a new tab) ↗
Read the result
Find the smallest positive denominator that is a multiple of all three inputs.
The primary result is labeled “Least common denominator”. Keep the input definitions in view when comparing this result with another method.
Try a related calculation
Reduce your fractions first if you want the smallest denominator of their reduced forms.
For a related exercise, try the fraction calculator.
A few questions, answered
How can I check the default inputs by hand?
The smallest common multiple of 6, 8, and 9 is 72.
Which rule does this calculator apply?
LCD = lcm(lcm(b,d),f)