Significant figures

Another way of rounding numbers is to count only the first few digits (maybe \(1\), \(2\) or \(3\) figures) that have a value attached to them. This method of rounding is called significant figures and it’s often used with larger numbers, or very small numbers.

Rounding \(12.756\) or \(4.543\) to one decimal place seems sensible, as the rounded figures are roughly equal to the actual value.

\(12.756 = 12.8\) (\(1\) decimal place)

\(4.543 = 4.5\) (\(1\) decimal place)

But what happens if you round a very small number to one decimal place?

\(0.00546 = 0.0\) (\(1\) decimal place)

\(0.00213 = 0.0\) (\(1\) decimal place)

This is not a useful answer. Another way to find an approximate answer with very small numbers is to use significant figures.

Counting significant figures

Significant figures start at the first non-zero number, so ignore the zeros at the front, but not the ones in between. Look at the following examples: