http://www.ck12.org Chapter 1. Introduction to Physical Science
1.29 Significant Figures
- Define significant figures.
- State rules for counting significant figures.
- Explain how to determine significant figures in calculations.
- Identify rules for rounding numbers.
Jerod has a homework problem that involves finding the area of a rectangle. He knows that the area of a rectangle
equals its length times its width. The rectangle in question has a length of 6.9 m and a width of 6.5 m, so he
multiplies the two numbers on his calculator. The answer he gets is 44.85 m^2 , which he records on his homework.
To his surprise, his teacher marks this answer wrong. The reason? The answer has too many significant figures.
What Are Significant Figures?
In any measurement, the number ofsignificant figuresis the number of digits thought to be correct by the person
doing the measuring. It includes all digits that can be read directly from the measuring device plus one estimated
digit.
Look at the sketch of a beaker below. How much blue liquid does the beaker contain? The top of the liquid
falls between the mark for 40 mL and 50 mL, but it’s closer to 50 mL. A reasonable estimate is 47 mL. In this
measurement, the first digit (4) is known for certain and the second digit (7) is an estimate, so the measurement has
two significant figures.