Using LCM to find a common denominator
Build equivalent fractions using the smallest shared denominator.
By the ClearLCM team · Updated November 3, 2026
Find the LCM of the denominators
To add 1/6 and 1/8, first find LCM(6, 8). Their GCF is 2, so (6 ÷ 2) × 8 = 24. A denominator of 48 would also be shared, but 24 is the least common denominator. Working with the smaller shared denominator often keeps the arithmetic easier.
Scale each fraction correctly
Convert 1/6 to twenty-fourths by multiplying both numerator and denominator by 4: 1/6 = 4/24. Convert 1/8 by multiplying both parts by 3: 1/8 = 3/24. Now add the numerators to get 7/24. Changing only the denominator would change the value of a fraction, so always apply the same multiplier to its numerator.
Reduce first when useful
If fractions have not been simplified, reducing them can make the denominator calculation smaller. The tool calculates the LCM of the integers you enter; it does not parse fractions or automatically simplify numerator-denominator pairs. Enter 6 and 8 for this example, rather than “1/6, 1/8.” For three fractions, enter all three positive denominators and convert each numerator separately. A zero denominator is not a valid fraction even though the LCM calculator describes a zero-input convention.
Put the example into practice with the free least common multiple calculator.