A quadrillion is a number equal to 1 followed by 15 zeros. It is equivalent to a thousand trillion or a million billion. The prefix "peta-" means a quadrillion. In the American system, the Latin prefix refers to the number of groups of three zeros, not including the last group of three, which represents a thousand. Thus in the USA, a billion is 1,000,000,000 (10^9) and a quadrillion is 1,000,000,000,000,000 (10^15). In the British system, the Latin prefix represents the power of a million, thus a British billion is 1,000,000,000,000 (10^12) and a British quadrillion is 1,000,000,000,000,000,000,000,000 (10^24) .