One trillion is 1,000 billions. One trillion is a one followed by 12 zeros, whereas one billion is a one followed by nine zeros. To add three zeros, multiply one billion by the number with three zeros, which happens to be 1,000.
One trillion is also equal to one million millions. There are 1,000 millions in one billion. Instead of counting the number of places, count the number of commas to determine the place value of a numeral. Commas are placed every three places from the right. One comma denotes entering the thousands; numbers in the trillions have four commas.