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The logarithm is a function related to powers of 10. If

then

Thus the logarithm of a number (in this case the logarithm of x) is the power to which 10 must be raised to get that number. If y is an integer (whole number) this is straightforward:

The idea can also be extended to numbers other than exact powers of 10. For example

Logarithms can be calculated on a scientific calculator using the log function. (Note this is generally indicated by log or log₁₀. It should not be confused with the "natural logarithm" function, written as either ln or log_e, which is irrelevant to decibels.)

Logarithms have a number of useful properties which come directly from properties of powers of 10. Thus the logarithm of a product (i.e. two numbers multiplied together) is simply the sum of their logarithms, and a similar relationship exists for the logarithm of a ratio: