Logarithm Calculator
Calculate logarithms in any base, including common log and natural log, free and instant right in your browser.
Enter Values
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How to use this calculator
- Enter the number and (optionally) the base.
- Press Calculate.
How it works
A logarithm answers 'what power gives this number?': log_base(number) = ln(number) ÷ ln(base). Base defaults to 10.
Worked example
log₁₀(1000). = 3.
Frequently asked questions
What's the difference between log and ln?
'ln' is the natural log (base e ≈ 2.718); 'log' usually means base 10. This tool lets you set any base, defaulting to 10.
Why can't I take the log of zero or a negative?
Logarithms are only defined for positive numbers — no power of a positive base gives zero or a negative result.
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Cite this tool
Zerdly. (2026). Logarithm Calculator. Retrieved from https://www.zerdly.com/tools/logarithm-calculator/
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.