Approximate measurements - Intermediate & Higher tier – WJECRounding to significant figures – Higher tier

The method of rounding to a significant figure is often used as it can be applied to any kind of number, regardless of how big or small it is. When a newspaper reports a lottery winner has won £3 million, this has probably been rounded to one significant figure. It rounds to the most important figure in the number.

To round to a significant figure:

1. look at the first non-zero digit if rounding to one significant figure
2. look at the digit after the first non-zero digit if rounding to two significant figures
3. draw a vertical line after the place value digit that is required
4. look at the next digit
5. if it’s 5 or more, increase the previous digit by 1
6. if it’s 4 or less, keep the previous digit the same
7. fill any spaces to the right of the line with zeros, stopping at the decimal point if there is one

Examples

Round 53,879 to one and two significant figures.

• 5|3879 to one significant figure is 50,000
• 53|879 to two significant figures is 54,000

Notice that the number of significant figures in the question is the maximum number of non-zero digits in your answer.

Round 0.005089 to one and two significant figures.

• 0.005|089 to one significant figure is 0.005
• 0.0050|89 to two significant figures is 0.0051