Count significant figures in any number and round to any number of significant figures, including scientific notation.
Count mode reads the number exactly as typed, so trailing zeros after a decimal point count. Rounding uses standard half-up rounding.
significant figures
How to use this tool
Keep trailing zeros and decimal points exactly as they appear — in 0.00450 the trailing zero counts, so the count is 3.
Enter 1 to 21. The rounded result is shown in ordinary and scientific notation.
The big number is the significant-figure count of your original input, before any rounding.
Copy the rounded result for lab reports and calculations where the precision of your measurements must be respected.
Formula & worked example
0.00450 has 3 significant figures (4, 5 and the trailing 0). Rounded to 2 significant figures, 0.004567 becomes 0.0046; 12345 rounded to 3 significant figures becomes 1.23×10⁴.
Limitations — read this before you rely on it
A plain integer such as 1200 is ambiguous in print: without a decimal point or scientific notation this calculator counts it as 2 significant figures, since trailing zeros in an integer may be placeholders. Write 1200. or 1.200×10³ if the zeros are meant to be significant. This tool counts and rounds; it does not propagate measurement uncertainty through calculations.
Frequently asked questions
The digits in a number that carry real meaning about its precision — starting from the first non-zero digit. In 0.00450, the significant figures are 4, 5 and the final 0, giving 3.
After a decimal point, yes: 120.0 has 4 significant figures. In an integer with no decimal point, trailing zeros are treated as placeholders, so 1200 counts as 2 unless written as 1200. or in scientific notation.
Keep the first three significant digits and round the rest: 0.004567 to 3 figures is 0.00457, and 12345 to 3 figures is 1.23×10⁴.
Every digit in the coefficient counts, including trailing zeros: 1.200×10³ has 4 significant figures, while 1.2×10³ has 2. Type numbers like 1.200e3 to use this form.
Zero on its own carries no non-zero digit to count from, so it is reported as 1 by convention. In a measurement context, 0.0 would instead be reported with the precision its decimal places imply.