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Logarithm (Log) Calculator

Compute logarithms in any base: y = logb(x). Use the quick base toggle (10, e, 2, or custom), get steps (change-of-base), quick picks, and a mini log curve visual.

Background

A logarithm answers: “what power do I raise the base to, to get the argument?” If by = x, then y = logb(x). Logs are only defined for x > 0, and the base must satisfy b > 0 and b ≠ 1.

Enter values

Tip: Base 10 is “log”, base e is “ln”, base 2 is common in CS.

Must be > 0. Logs of negative numbers aren’t real.

Options

We also auto-switch to scientific notation for huge/small values.

Chips prefill values and calculate immediately.

Result

No results yet. Enter values and click Calculate.

How to use this calculator

  • Choose the base using the quick toggle (10, e, 2, or custom).
  • Enter the argument x (must be > 0).
  • Click Calculate to get the value, steps, and the curve visual.

How this calculator works

  • Definition: If by = x, then y = logb(x).
  • Change of base: logb(x) = ln(x)/ln(b) (works for any valid base).
  • Domain: x > 0, b > 0, and b ≠ 1.

Formula & Equation Used

Log definition: y = logb(x) ⇔ by = x

Change of base: logb(x) = ln(x)/ln(b)

Example Problems & Step-by-Step Solutions

Example 1 — log10(1000)

  1. Base b = 10, argument x = 1000.
  2. Because 103 = 1000, we get log10(1000) = 3.

Example 2 — log2(1/8)

  1. x = 1/8 = 2-3.
  2. So log2(1/8) = -3.

Example 3 — Change of base

  1. To compute log3(10), use ln(10)/ln(3).
  2. This gives a decimal approximation.

Frequently Asked Questions

Q: Why must x be positive?

Because by is positive for any real y when b>0.

Q: Why can’t the base be 1?

Because 1y = 1 for all y, so it can’t uniquely “undo” exponentials.

Q: What’s the difference between log and ln?

log(x) usually means base 10, while ln(x) is base e.

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