About this tool
The Significant Figures Calculator is a free, in-browser tool that counts how many significant figures a number has as written and rounds it to any number of significant figures you choose. It also shows the value in scientific notation and lists exactly which sig-fig rules were applied to your number.
Type the number as text — including any trailing zeros, which matter for significant figures — and the count, the rounded value and the scientific form update instantly. Numbers in e-notation such as 1.23e4 are supported, and everything is computed locally in your browser with nothing uploaded.
Frequently asked questions
Which digits are significant?
All non-zero digits, zeros between non-zero digits, and trailing zeros after a decimal point are significant. Leading zeros are never significant — they only locate the decimal point.
Why does 1200 show only 2 significant figures?
Trailing zeros in a whole number written without a decimal point are ambiguous, and by convention this tool treats them as not significant. Write 1200. , 1.200e3 or 1.2e3 to make the intended precision explicit.
Why must I type the number instead of pasting a computed value?
Significant figures depend on how the number is written, not just its value — 2.50 and 2.5 are numerically equal but have 3 and 2 sig figs. The tool therefore reads your input as text to preserve trailing zeros.
How does rounding to N significant figures work?
The tool keeps the N leading significant digits and rounds the rest using standard round-half-up-style rounding, adjusting the magnitude as needed — e.g. 0.004560 rounded to 2 sig figs is 0.0046.