Calculators
Significant Figures Calculator
Count the significant figures in a number and round it to a chosen number of significant figures, with leading, middle, and trailing zero rules explained, locally in your browser.
Count how many significant figures a number has, then optionally round it to a chosen number of significant figures. Leading zeros never count, zeros between non-zero digits always count, and trailing zeros count only when a decimal point is written. Scientific notation such as 6.022e23 is accepted. Everything runs locally in your browser; your values are not uploaded or stored.
Count significant figures and round a number to any precision.
Enter a number using digits, an optional decimal point, and optional e-notation such as 6.022e23, then optionally enter how many significant figures to round to (1–15). The calculator reports how many significant figures the input has and, when a rounding value is given, the rounded result plus its scientific notation. The counting rules are: leading zeros are never significant, zeros between non-zero digits are always significant, and trailing zeros count only when a decimal point is written. For example, 0.00410 has three significant figures (4, 1, 0), 1000 has one by the usual whole-number convention (its trailing zeros are ambiguous), 1000. has four, and 6.022e23 has four. Rounding keeps the requested number of significant figures, so 0.0999 rounded to two significant figures is 0.10 and 12345 rounded to two is 12000, or 1.2 × 10^4. Numbers up to 100 digits are accepted, and missing, malformed, or out-of-range entries show a clear message instead of a misleading result. All processing stays in your browser.
Frequently Asked Questions
Everything you need to know about this tool, how it works, and privacy.
How does the calculator count significant figures?
It applies the standard rules: all non-zero digits are significant; zeros between non-zero digits are significant; leading zeros that only set the position of the decimal point are not significant; and trailing zeros are significant only when a decimal point is written. So 0.00410 has three significant figures, 1.230 has four, and 1500. has four.
Why is the count for a whole number like 1500 ambiguous?
A whole number such as 1500 written without a decimal point does not show whether its trailing zeros are measured or just placeholders, so its significant figures are ambiguous. The calculator treats those trailing zeros as not significant, which gives 2, and flags the ambiguity. Write 1500. or 1.500 x 10^3 to indicate four significant figures clearly.
How does rounding to significant figures work?
Enter a target between 1 and 15. The calculator keeps that many significant digits and rounds the first discarded digit up when it is 5 or more. For example, 0.0999 to two significant figures is 0.10, 12345 to two significant figures is 12000 (1.2 x 10^4), and 12.345 to four significant figures is 12.35.
Does the calculator accept scientific notation?
Yes. You can enter numbers such as 6.022e23 or 1.0e-5. The digits in the coefficient are counted directly, so 6.022e23 has four significant figures and 1.0e-5 has two. Every digit of the coefficient counts, including trailing zeros after the decimal point.
What happens with zero or invalid input?
A value of zero has no non-zero digits, so the calculator explains that its significant figures are not defined by the standard rules rather than returning a misleading number. Missing, non-numeric, or oversized entries (more than 100 digits, or a magnitude outside about 1e-300 to 1e300 for rounding) show a clear message. The calculation and copy run locally in your browser; CodeASystem does not upload or store your values.