The LCM (Least Common Multiple) is the smallest number both numbers divide into. Three ways to find it:
1. List multiples
Multiples of 4: 4, 8, 12… Multiples of 6: 6, 12… → LCM(4, 6) = 12. Fine for small numbers.
2. Prime factorization
12 = 2² × 3, 18 = 2 × 3². Take the highest power of each prime: 2² × 3² = 36.
3. The GCD shortcut (fastest)
LCM(a, b) = a × b ÷ GCD(a, b). GCD(12, 18) = 6, so LCM = 12 × 18 ÷ 6 = 36.
Our LCM calculator uses the GCD method instantly — it also gives you the GCF, which is what simplifies fractions in our fraction calculator.