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Significant Figures Counter

Count the significant figures in any number with every digit classified by rule, or round a number to 1–15 significant figures with exact string-based math.

Processing... 0%
Parsing the number
Classifying every digit
Applying the sig-fig rules

Result

This page opens the sig fig calculator in counting mode: paste any number and it returns the number of significant figures, with every single digit highlighted and labelled by the rule that decides its fate.

The rules the counter applies are the standard four. Nonzero digits always count. Zeros trapped between significant digits — captive zeros, like the 0 in 4.05 — always count. Leading zeros, like the three in 0.004560, never count: they only fix the decimal scale. Trailing zeros count only when the number has a decimal point, which is why 0.004560 has 4 significant figures but 1200 conventionally has just 2.

That last case is flagged honestly: for a whole number ending in zeros the counter reports the conventional minimum, notes that the true count could be higher if the value was measured exactly, and shows the scientific notation — 1.200 × 10³ — that would state the precision beyond doubt. Everything runs locally in your browser.

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Executed in Browser

Your files and inputs never leave this device. Processing runs completely offline. 100% Secure.

Accepted Formats & Rules

  • Counter mode: per-digit classification — nonzero, captive zero, leading zero, trailing zero with or without a decimal point.
  • Rounding mode: 1 to 15 significant figures with digit-string math, so 0.0019997 becomes 0.00200 with its trailing zeros intact.
  • Optional scientific notation output, like 1.20 × 10³.
  • Honest notes for the tricky cases: the number zero and integers ending in zeros.

Key Benefits

✓ Every digit is highlighted and labelled with the exact rule that makes it significant or not — you learn the why, not just the count.
✓ Ambiguity is flagged honestly: trailing zeros in 1200 are called out as ambiguous, with the scientific notation that would resolve them.
✓ Runs entirely in your browser: no sign-up, no upload, instant results.

Use Cases

  • • Check chemistry and physics homework: count the sig figs in a measurement and see the rule behind every digit.
  • • Round lab results to 2, 3 or 4 significant figures with digit-exact math — 0.0019997 keeps its trailing zeros as 0.00200.
  • • Resolve ambiguous integers like 1200 by switching to scientific notation such as 1.200 × 10³.