Significant figures

Count the significant figures in a number and round it to any digit count.

Rules: nonzero digits always count; zeros between significant digits count; leading zeros never count; trailing zeros count only when a decimal point is shown.

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How to use

  1. Enter a number — decimals and e-notation work.
  2. Pick the round-to digit count.
  3. Read the count, rounded value, and which rule applied.

What it supports

Counts sig figs by the standard classroom rules; trailing zeros in a bare integer (like 1500) are reported as ambiguous and counted as not significant — write 1.5e3 to make them significant. Arithmetic sig-fig propagation (keep the least digits) is not performed.

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