Logarithm calculator
Enter a value and a base to get log, plus ln, log₁₀ and log₂.
Logarithm calculator
Calculate the logarithm of a number in any base, and instantly see the natural log (ln), log₁₀ and log₂. A logarithm answers “what power must the base be raised to, to get this number?”.
Formula
logb(x) = ln(x) ÷ ln(b). Example: log₁₀(100) = 2 because 10² = 100; log₂(8) = 3 because 2³ = 8. The input must be greater than zero — logarithms of zero or negatives are undefined.
Frequently asked questions
What is the difference between log and ln? “log” usually means base 10; “ln” is the natural log, base e (≈2.718).
Why can’t I take the log of a negative number? No real power of a positive base gives a negative result, so it’s undefined over the reals.