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Round to 4 Significant Figures Calculator

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 preset to round to 4 significant figures, a precision fine enough for engineering constants and most tabulated physical data — π at four figures is 3.142, e is 2.718.

The fifth significant digit makes the call. 3.14159 keeps 3, 1, 4, 1 and the next digit is 5, so the last kept digit rises: 3.142. Carries chain cleanly through nines: 999.97 to four figures rolls over to 1000, and the tool notes that this particular result hides its own precision — written plainly, 1000 could mean anything from 1 to 4 significant figures.

That is exactly when the scientific notation option earns its place: 1.000 × 10³ says four significant figures and nothing else. The rounding operates on the digits you typed, so no floating-point representation error can creep into the last figure. All of it 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.