With one number "a" and another smaller number "b", the ratio of the two numbers is found by dividing them. Their ratio is "a"/"b". Another ratio is found by adding the two numbers together and dividing this by the larger number "a". The new ratio is ("a"+"b")/"a". If these two ratios are equal to the same number, then that number is called the golden ratio. The Greek letter formula_1 (phi) is usually used as the name for the golden ratio.