Which digits count
Not every digit in a number is significant. The rules are consistent once you learn them: all non-zero digits count, zeros between non-zero digits count, and trailing zeros count only when there is a decimal point. Leading zeros never count — they merely place the decimal.
Scientific notation removes the ambiguity entirely, because every digit written in the mantissa is significant by construction.
- 1234 has 4 significant figures.
- 0.00230 has 3 (the leading zeros do not count, the trailing zero does).
- 100 is treated as 1 significant figure under the common convention.
Reading the result
The calculator reports how many significant figures your input already has, the value rounded to the precision you asked for, and that rounded value in scientific notation.
Why it matters
Significant figures communicate how precise a measurement is. Reporting more digits than your instrument can resolve overstates certainty; reporting too few throws away real information. In science and engineering the answer to a calculation should carry no more significant figures than the least precise input.
Common mistakes
The trickiest cases are zeros. Remember that trailing zeros are only significant when a decimal point is present, and that leading zeros are never significant regardless of where the decimal sits.
Formula
rounded = value to N significant figuresFrequently asked questions
- Is 100 one or three significant figures?
- Written plainly, 100 is treated as one significant figure. To show three, write it with a decimal point (100.) or in scientific notation as 1.00 × 10².