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Round to 3 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 3 significant figures — the workhorse precision of chemistry and physics classes, where three figures usually matches the accuracy of the measuring gear.

Counting starts at the first nonzero digit, and the fourth significant digit decides the rounding. So 3.14159 keeps 3, 1, 4 and looks at the second 1: it rounds down, giving 3.14. The interesting case is 0.0019997: the three significant digits are 1, 9, 9, the next 9 forces a cascade of carries, and the answer is 0.00200. Those two trailing zeros are not decoration — at three significant figures they are genuinely significant, and this calculator keeps them because it rounds the digit string rather than a float.

Tick the scientific notation option to get answers like 2.00 × 10⁻³, the format that makes precision unambiguous in lab reports. Everything is computed locally in your browser, and one click copies the result.

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Executed in Browser

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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.