This free online log calculator finds the logarithm of any number to a base of your choosing, or the natural log (ln) when you need it. Enter the number and base, or toggle natural log, to get an accurate result instantly.
How to Use the Log Calculator
Enter the number (x) you want to find the logarithm of in the "Number (x)" field.
Enter the base (b) in the "Base (b)" field, for example 10 or 2.
Check "Natural log (ln)" instead if you want the base to be e.
Click "Calculate" to see the result instantly.
Frequently Asked Questions
For a base-10 log it uses log10(x); for a custom base b it uses the change-of-base formula logb(x) = ln(x) / ln(b). When "Natural log (ln)" is checked, it calculates ln(x) directly. For example, log2(8) = 3.
Logarithms are only defined for positive numbers, so the calculator shows "Number must be greater than 0" if you enter zero or a negative value for x.
A base of 1 or a base that is zero or negative makes the logarithm mathematically undefined, so the calculator shows "Base cannot be 1" or "Base must be greater than 0" accordingly.
Yes, it's completely free and requires no sign-up.