Significant Figures Calculator — How to Count and Round Sig Figs
Count significant figures in a number string or round to N sig figs. Leading zeros do not count; trailing zeros after a decimal do. Example: 0.00304 → 3 sig figs; round 1234.56 to 3 → 1230 (1.23e3). Half away from zero. Runs in your browser to calculate and check homework.
How it works
Choose Count or Round. Paste the number as text so leading zeros stay visible. Count returns how many sig figs; Round needs N and shows a decimal string plus scientific form like 1.23e3.
Rules documented here
Standard school counting and half-away rounding:
- Non-zero digits always count; zeros between them count.
- Leading zeros never count (0.00304 → 3).
- Trailing zeros after a decimal count; bare trailing zeros in integers without a decimal do not.
- Rounding: scale mantissa to N digits; halfway cases move away from zero (positives half-up).
Example
Count 0.00304 → 3. Round 1234.56 to 3 → 1230 and 1.23e3.
When to use it
- Lab homework: check how many sig figs a measurement string carries.
- Round a calculated result to the allowed precision.
- Compare ordinary and scientific displays of the same round.
Frequently asked questions
Do leading zeros count?
No. In 0.00304 only 3, 0, and 4 count → 3.
What about trailing zeros in 1200?
Without a decimal point this page does not count them (2 sig figs).
How is halfway rounded?
Away from zero; for positives that is half-up.
Why keep the input as text?
So forms like 0.00304 keep visible leading zeros for counting.
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Questions or feedback
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