Significant Figures Calculator

What are significant figures?

Significant figures — often shortened to "sig figs" — are the digits in a number that carry real information about its precision. They include every certain digit plus the first uncertain one. This calculator does two jobs: it counts how many significant figures a number has, and it rounds any value to the number of significant figures you choose, using the standard rules taught in science, engineering, and chemistry. For related work with very large or small numbers, see the scientific notation converter.

How to count significant figures

Four rules cover almost every case. First, every non-zero digit is significant, so 4.72 has three. Second, any zeros between non-zero digits are significant, so 1,005 has four. Third, leading zeros are never significant — they only place the decimal point — so 0.0025 has just two. Fourth, trailing zeros are significant only when the number contains a decimal point: 1200 has two significant figures, but 1200. and 12.00 each have four. To round to a set number of sig figs, keep that many significant digits, round the rest using the normal "5 rounds up" rule, and pad with placeholder zeros if the number is large. When you work with powers, the exponent calculator helps you compute the underlying values before rounding, and the standard deviation calculator shows how precision propagates through a data set.

Example

Take 0.004560. The three leading zeros don't count, but the trailing zero sits after the decimal point, so the number has four significant figures. Rounding 3.14159 to three significant figures gives 3.14, and rounding 12345 to three gives 12300. Because 12300 has no decimal point, those final two zeros are placeholders rather than significant digits.