Significant Figures Rounding Calculator

Significant figures are the digits in a number that carry meaning about its precision. They include all nonzero digits, any zeros between nonzero digits, and trailing zeros in a number with a decimal point. Leading zeros are never significant. For example, 0.004560 has four significant figures: the 4, 5, 6 and the trailing zero, while the leading zeros only set the decimal place.

Identify the first significant digit, count along to the chosen number of significant figures, then look at the next digit to decide whether to round up or down. If that next digit is 5 or more, round up; otherwise keep the figure as is. For example, 3,141.59 rounded to three significant figures is 3,140, because the fourth significant digit (1) is less than 5.

Significant figures express precision relative to the size of a number, which matters in science and engineering where measurements span many orders of magnitude. Rounding to a fixed number of decimal places can lose all meaning for very small or very large numbers. Significant figures keep the relative precision consistent: three significant figures convey the same relative accuracy whether the value is 0.00321 or 32,100.

Scientific notation writes a number as a single nonzero digit, a decimal fraction, and a power of ten, for example 3.14e3. The digits before the power of ten are exactly the significant figures, which is why scientific notation makes the count unambiguous. This calculator shows the rounded result in both ordinary and scientific notation so the significant figures are clear.