Sig Fig Calculator

Rules for counting significant figures

Significant figures (sig figs) are the digits of a measurement that carry meaning about its precision. All non-zero digits are significant. Zeros between non-zero digits are significant, so 3005 has four. Leading zeros are never significant: 0.00340 has three significant figures, because the zeros in front only place the decimal point. Trailing zeros are significant when the number contains a decimal point, so 0.00340, 2.50 and 1200. all show that the last zero was measured. In a whole number such as 1200 with no decimal point, trailing zeros are ambiguous. This calculator treats them as not significant and highlights each significant digit so you can see exactly how the count was made.

Rounding and scientific notation

To round to a set number of significant figures, keep that many digits starting from the first non-zero digit and round the last one. 0.0034567 rounded to three sig figs is 0.00346, and 1234.5 rounded to two is 1200. Sometimes the plain result can't show its precision: 1004 rounded to three sig figs is 1000, which looks like one significant figure. Scientific notation removes the ambiguity, so the calculator also shows 1.00 × 10³. You can enter values in scientific notation too, using forms like 1.20e3 or 4.5×10^-3.

Significant figures in calculations

A result can't be more precise than the data it comes from. For multiplication and division, the answer keeps the smallest number of significant figures found in the inputs: 2.5 × 3.42 = 8.55, which is reported as 8.6 because 2.5 has only two. For addition and subtraction, what matters is decimal places: round to the least precise place among the inputs, so 12.11 + 18.0 = 30.11 becomes 30.1. Subtraction can lose many significant figures, as in 5.00 − 4.99 = 0.01. For multi-step problems, keep extra digits in intermediate steps and round only the final answer to avoid accumulated rounding error. Everything runs locally in your browser.