To determine their equivalence, we simplify both ratios by dividing each number by their greatest common divisor.

For the ratio 18:6, the greatest common divisor of 18 and 6 is 6. Dividing both numbers by 6, we get 3:1 as the simplified form.

Similarly, for the ratio 36:12, the greatest common divisor of 36 and 12 is 12. Dividing both numbers by 12, we also get the simplified form as 3:1.

Since both ratios simplify to the same value of 3:1, we can conclude that 18:6 is indeed equivalent to 36:12.