 Site Navigation                          Science: Significant Figures - Rules and Practice

What are significant digits? Significant digits indicate how much care was taken in making a measurement. They also indicate how much precision is available in the tool used to make a measurement. For example, the triple beam balance, when used correctly, will allow you to measure an object's mass to the hundredth of a gram. Many students, however, will be careless and record the mass only to the tenths place.

Example: A student was asked to find the mass of a penny using a triple beam balance. Which measurement shows the mass recorded as accurately as the balance will allow? How many significant digits are in the measurement?

mass of copper penny = 3.15 g

or

mass of penny = 3.2 g

Answer:  Since the balance can measure to hundredths, 3.15 g shows that the tool was used with care. The correct measurement has 3 significant figures. The sloppy measurement has only 2 significant figures.

The Rules:

1. If a number does not have a decimal point, then zeros at the end of the number are place holders. These digits are not significant.

Example: 55,000 meters

This number was measured to 2 significant digits. The zeros at the end of this measurement are just place holders.

1. If the number begins with a decimal, the zeros at the end are significant.

Example: 0.88000 meters

This number has 5 significant digits. The zeros at the end tell us that the measurement was done with a precise tool.

When a measurement is written down, you should be able to tell how many digits of the measurement are significant, or measured. Let's focus in this drill on numbers that begin or end with zeros.

Question Group #1
Directions and/or Common Information: How many significant figures are in each of these measurements?
 0.075 g
 1

 15,100 mL
 2

 12,000 cm3
 3

 0.0000056 inches
 4

 0.01123 grams
 5

 10,000,000 sheets of paper
 6

 533,000 coins
 7

 0.00088 cm
 8

 0.00761 liters
 9

 110 meters
 10

Question Group #2
Directions and/or Common Information: Now try a few that have zeros at the beginning and the end.
 0.000876
 1

 32,000.0
 2

 0.0987
 3

 4e-07
 4

 5,400.0
 5

E Saylor

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