Significant figures calculator
The number 1200 might have two significant figures or four, and written that way there is no way to tell. A decimal point settles it — 1200. has four — and scientific notation settles it unambiguously: 1.2 × 10³ is two, 1.200 × 10³ is four. That is a large part of why scientific notation exists at all, and why measurement data should be written in it.
Significant figures count the digits that carry meaning. 3.14159 to three significant figures is 3.14. Leading zeros never count, zeros between digits always do, and trailing zeros count only after a decimal point.
How to use significant figures
In calculations, the rules differ by operation. Multiplication and division keep the significant figures of the least precise input, so 2.0 × 3.14159 gives 6.3 rather than 6.28318. Addition and subtraction work on decimal places instead — 12.11 + 0.3 gives 12.4, because the second value is only known to one decimal. Applying the multiplication rule to addition is the most common error, and it produces answers that claim more precision than the data supports.
Questions
Three. Leading zeros never count; the trailing zero after a decimal point does.