Rounds a number to a chosen number of significant figures, following the standard scientific convention.
How it works
The number’s order of magnitude is found first, then it’s rounded to the requested number of significant digits from its first nonzero digit.
What this does not include
This does not include scientific-notation formatting of the result — the rounded value is shown in standard decimal form.
How to use this calculator
- Enter a number and how many significant figures to round to.
A worked example
123.456 rounded to 3 significant figures → 123.
0.004567 rounded to 2 significant figures → 0.0046 — leading zeros before the first nonzero digit don’t count toward the significant figure total.
What the variables mean
| Variable | Meaning |
|---|---|
| Value | The number being rounded |
| Significant figures | How many meaningful digits to keep, starting from the first nonzero digit |
Edge cases worth knowing
Leading zeros are never significant, but trailing zeros after a decimal point are. 0.0046 has exactly 2 significant figures — the leading zeros just place the decimal point.
Significant figures aren’t the same as decimal places. 123.456 to 3 sig figs is 123 (zero decimal places), while 0.004567 to 2 sig figs is 0.0046 (four decimal places) — the rule tracks meaningful digits, not a fixed position after the decimal.
Frequently asked questions
Why don’t leading zeros count as significant figures?
Leading zeros (like the 0 in 0.0046) only indicate the position of the decimal point, not measurement precision, so they’re excluded from the significant figure count.
Do trailing zeros after a decimal point count?
Yes — a number like 1.230 has 4 significant figures, since the trailing zero after the decimal indicates measured precision to that digit.
Where are significant figures commonly used?
Scientific measurements and lab reports, where the number of significant figures communicates how precisely a value was actually measured.
