Identify the denominators. The denominator is the number on the bottom of a fraction; the number on the top of the fraction is called the numerator. For example. the denominator of 1/3 is 3; the denominator or 5/16 is 16.
Write out the factors of each denominator. The factors of a denominator are like the factors for any other integer: all of the numbers that divide evenly into it. For example, the factors of 16 are 1, 2, 4, 8 and 16; the factors of 24 are 1, 2, 3, 4, 6, 8, 12 and 24.
Identify the greatest common factor (GCF) of the two denominators. The GCF is just what it sounds like: the largest number that's a factor of both. For example, the GCF of 16 and 24 is 8, as it is the largest number that's a factor of both 16 and 24.
Multiply the denominators of the two fractions, then divide the product by their greatest common factor. For example, to find the lowest common denominator of 1/16 and 1/24, multiply the denominators:
16 * 24 = 384
The GCF of 16 and 24 is 8, so divide the result by 8:
384 / 8 = 48
The LCD of 1/16 and 1/24 is 48.