This is a free math calculator, which is able to calculate the logarithm for a number to a base. You can also choose the base. The best mathematical tool for school and college! If you are a student, it will helps you to learn algebra. Note: The logarithm of a number is the exponent to which another fixed value, the base, must be raised to produce that number. For example, the logarithm of 1000 to base 10 is 3.