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Least Common Multiple Calculator

Please provide numbers separated by a comma "," and click the "Calculate" button to find the LCM.

Supports 2 or more whole integers (e.g. 12, 18, 24, 30).
Quick Presets:

What is the Least Common Multiple (LCM)?

In elementary number theory and arithmetic, the Least Common Multiple (denoted as LCM, or lowest common multiple / smallest common multiple) of two or more non-zero integers a and b is the smallest positive integer that is divisible by both a and b without leaving a remainder.

For instance, consider the integers 4 and 6:

  • Multiples of 4: 4, 8, 12, 16, 20, 24, 28, 32, 36, ...
  • Multiples of 6: 6, 12, 18, 24, 30, 36, 42, ...

The common multiples are 12, 24, 36, ... and the least among them is 12. Thus, LCM(4, 6) = 12.

4 Methods to Find the Least Common Multiple

1. Prime Factorization Method

Most Reliable

Break each integer down into powers of its prime factors. The LCM is the product of the highest power of every prime factor appearing across any number:

LCM = p₁^(max e₁) × p₂^(max e₂) × ... × pₖ^(max eₖ)

2. Greatest Common Divisor (GCD) Formula

Fastest Algorithm

Using the Euclidean algorithm, compute the GCD of the numbers. The product of two numbers divided by their GCD gives their LCM:

LCM(a, b) = |a × b| / GCD(a, b)

3. Common Division (Cake / Ladder) Method

Visual Ladder

Place the numbers in an upside-down division bracket. Repeatedly divide by prime numbers that divide at least two numbers. Multiply all divisors on the left by the numbers in the final bottom row.

4. Listing Multiples (Brute Force)

Small Sets

List the consecutive multiples of each number (a, 2a, 3a, 4a, ...) until the first common integer appears in all lists. Ideal for mental math with small numbers.

Practical Applications of the Least Common Multiple

➗ Fractions & LCD

Finding the Least Common Denominator (LCD) when adding or subtracting fractions with unlike denominators is identical to finding the LCM of the denominators.

⏱️ Synchronizing Periodic Events

Determining when multiple periodic events will occur simultaneously (e.g. traffic lights cycling every 45s and 60s, or buses arriving at a shared stop).

⚙️ Gear Ratios & Planetary Meshing

Mechanical engineers calculate how many tooth revolutions must occur before identical teeth on meshing gears touch again using the LCM of their tooth counts.

Frequently Asked Questions

What is the LCM of two prime numbers?

Because two distinct prime numbers share no common factors other than 1 (they are coprime, GCD = 1), their LCM is simply their direct product: LCM(p, q) = p × q. (e.g. LCM(7, 11) = 77).

What is the LCM of a number and 0?

By standard mathematical convention, LCM(a, 0) = 0, because 0 is a multiple of every integer (0 = k × 0).

How is the LCM related to the Greatest Common Factor (GCF)?

For any two positive integers a and b, the product of their LCM and GCF equals the product of the two numbers: LCM(a, b) × GCF(a, b) = a × b.