Significant Figures Calculator

Count the number of significant figures in any number, or round a number to a specific number of significant figures. Step-by-step explanations are included for each calculation.

Enter a Number

Include a trailing decimal point (e.g. 1200.) to indicate all zeros are significant.

What Are Significant Figures?

Significant figures (also called significant digits or sig figs) are the meaningful digits in a measured or calculated number. They communicate the precision of a measurement — the more significant figures, the more precise the value.

Rules for Counting Significant Figures

All non-zero digits are significant. In 1,234, all four digits are significant (4 sig figs).
Zeros between non-zero digits are significant. In 1,002, all four digits are significant (4 sig figs).
Leading zeros are NOT significant. In 0.0034, only 3 and 4 are significant (2 sig figs). Leading zeros are just placeholders.
Trailing zeros after a decimal point ARE significant. In 3.400, all four digits are significant (4 sig figs) — the trailing zeros indicate measured precision.
Trailing zeros in a whole number are ambiguous without a decimal point. The number 1200 may have 2, 3, or 4 sig figs. Writing 1200. (with decimal point) indicates 4 sig figs. Scientific notation removes all ambiguity: $1.2 \times 10^3$ has 2 sig figs.

Significant Figures in Calculations

When using measured values in calculations, the result should not be reported with more precision than the original measurements allow.

Multiplication and division: The result should have the same number of sig figs as the measurement with the fewest sig figs.
Example: $4.56 \times 1.4 = 6.384$ → rounds to $6.4$ (2 sig figs, matching the 2 in 1.4)
Addition and subtraction: The result should be rounded to the same number of decimal places as the measurement with the fewest decimal places.
Example: $12.11 + 18.0 + 1.013 = 31.123$ → rounds to $31.1$ (no more than one decimal place)

For converting results to scientific notation, try our scientific notation converter.

Frequently Asked Questions

Are exact numbers significant?

Exact numbers — like defined constants or counted quantities — have infinite significant figures and do not limit the precision of a calculation. For example, there are exactly 12 inches in a foot, and counting 15 students in a classroom is exact.

How many significant figures should I use in my answer?

In science coursework, use the same number of sig figs as the least precise measurement in your calculation. For general math or engineering, the context usually dictates the required precision — consult your instructor or project requirements.

Why do trailing zeros matter?

The difference between writing 2.50 and 2.5 is scientifically meaningful. Writing 2.50 g communicates that the measurement is precise to the hundredths place (3 sig figs), while 2.5 g only confirms precision to the tenths place (2 sig figs). Dropping or adding trailing zeros changes the implied precision of a measurement.