Count and round significant figures
Which digits carry precision and which are padding? Count significant figures in any written number and round to a chosen count.
Tools used in this guide
The job
A lab answer of 12.4389025 g looks precise but the balance only reads 0.01 g. Significant figures record how much of a written number is real measurement; the rest is arithmetic noise.
Count, then round
Enter a number — decimal or scientific notation — and read the count and which digits are significant. Set a target count to get the rounded value and the rule that applied.
- Leading zeros never count: 0.0031 has 2 sig figs.
- Trailing zeros without a decimal point are ambiguous — 1500 is reported as 2, write 1.5e3 or 1.50e3 to be exact.
Worked example
0.020450 has 5 significant figures (the trailing zero counts because a decimal point is present). Rounded to 3 sig figs it becomes 0.0204.
Where it stops
It counts and rounds a single number; it does not propagate sig figs through calculations or track uncertainties. Ambiguous trailing zeros are flagged rather than silently counted. Exact counts (3 people, defined constants) are not modeled.