Rex says
The fast lane for the math you almost remember from school. Type the numbers, get the answer, move on with your day.
Try a scenario
Click to load — tweak from there.Inputs
Result
log at your base
3.000000
Natural log (ln)
6.907755
Log base 10
3.000000
Log base 2
9.965784
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
How to use this
- 1Enter value (x).
- 2Enter base (b).
- 3Read your log at your base on the right — it updates as you type.
- 4Hit Share to keep the scenario or send it to someone.
About this calculator
A logarithm answers 'what power do I raise this base to?'. Logs at arbitrary bases are computed with the change-of-base rule.
Worked example
Using the values the calculator loads with:
Inputs
- Value (x): 1000
- Base (b): 10
Results
- log at your base: 3
- Natural log (ln): 6.907755
- Log base 10: 3
- Log base 2: 9.965784
What each field means
Inputs
- Value (x)
- The value (x) used in the calculation. Starts at 1000 so you have a working example on load.
- Base (b)
- The base (b) used in the calculation. Starts at 10 so you have a working example on load.
Results
- log at your base
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Natural log (ln)
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Log base 10
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Log base 2
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the logarithm calculator work?
A logarithm answers 'what power do I raise this base to?'. Logs at arbitrary bases are computed with the change-of-base rule. The underlying maths is: log_b(x) = ln(x) ÷ ln(b).
What do I need to enter?
2 values: value (x), and base (b). Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the log at your base result mean?
It is returned as a decimal number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Results are rounded for display; the underlying calculation keeps full precision.
Who is this tool for?
It's built for students, developers, and anyone who needs the answer right now without setting up a spreadsheet.
Accuracy and limitations
- Results are rounded for display; the underlying calculation keeps full precision.
- Very large or very small inputs may hit floating-point limits in the browser.
- Inputs outside the accepted range are clamped rather than rejected.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Logarithm Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/logarithm
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/logarithm" target="_blank" rel="noopener">Logarithm Calculator — RevenueLab</a> (2026).</p>
Source: [Logarithm Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/logarithm) (2026).