The arithmetic mean is the sum of the numbers divided by the number of numbers The geometric mean is the n root of the product of the numbers. For example, if the numbers you want to find the mean of are: 1 10 11 99 The arithmetic mean is 30.25, while the geometric mean is 10.21. The geometric mean is more accurate when the value are a bit skewed (in the example 99 is an outlier, and it brings the arithmetic mean all the way up to 30, which is not very representative of the 4 numbers, the geometric one is more accurate), while the arithmetic mean is the better one when the data is more uniform and independent of each other (the geometric mean is almost always lower)