Significant Figures Calculator

Round numbers to sig figs or count significant digits

Mode

Number

Significant figures

Rounded to 3 significant figures

12300

Scientific notation

1.23e+4

How significant figures work

Significant figures (sig figs) are the meaningful digits in a measured or calculated number. The rules: all non-zero digits are significant; zeros between non-zero digits are significant; leading zeros are never significant; trailing zeros after a decimal point are significant; trailing zeros in a whole number are ambiguous unless a decimal point is shown. When rounding to N sig figs, find the magnitude (log₁₀), then round to N−1−magnitude decimal places. Scientific notation always makes the count unambiguous.

Built and maintained by Meet Shah · Last updated 19 July 2026

What this tool is used for

Rounding a measurement to the precision the instrument justifies.
Counting the significant figures in a value from a datasheet.
Checking a reported result's precision against its inputs.
Rounding for a scientific report's convention.
Confirming a rounding you did by hand before submitting a result.

Frequently Asked Questions

Which digits are significant?: All non-zero digits; zeros BETWEEN them; and trailing zeros only when a decimal point is present. Leading zeros never count — 0.00420 has three significant figures, not five.
Why is 1500 ambiguous?: Because you cannot tell whether the trailing zeros were measured or are placeholders — it could be two, three or four significant figures. Scientific notation removes the ambiguity: 1.5 × 10³ is two, 1.500 × 10³ is four.
How do the rules differ for multiplication and addition?: Multiplication and division keep the fewest SIGNIFICANT FIGURES of any input. Addition and subtraction keep the fewest DECIMAL PLACES. Applying the multiplication rule to a sum is the most common mistake.
What is round-half-to-even?: Banker's rounding — 2.5 rounds to 2 and 3.5 rounds to 4, so ties go to the even digit. It exists because always rounding halves up introduces a systematic upward bias across a large dataset.
When should I round?: At the END of a calculation, never between steps. Rounding intermediate values compounds error, which is why scientific software carries full precision internally and rounds only for display.
Do exact and counted values limit the result?: No. A count of 12 objects or a defined conversion such as 2.54 cm per inch is exact and carries unlimited significant figures, so it never constrains the answer. Only measured quantities do.
How should intermediate steps be rounded?: They should not be. Carry full precision through the calculation and round once at the end, because rounding at each step compounds — a chain of five roundings can move the final digit by more than the reported uncertainty.
What is the difference between precision and accuracy?: Precision is how finely a value is reported, accuracy is how close it is to the truth. Significant figures track only the first, which is why a badly calibrated instrument can produce a very precise and entirely wrong number.

Common errors and gotchas

Reporting more figures than the least precise input justifies, which implies accuracy you do not have.
Miscounting leading zeros, which are never significant.
Miscounting trailing zeros before a decimal point, which are ambiguous without notation.
Rounding at each intermediate step rather than at the end, which accumulates error.
Confusing significant figures with decimal places, which are different rules.