Topic 6 of 8
Measuring in inches and centimeters
Step 4 · Place value to 1,000 topics
Measure with a ruler in inches and centimeters, see why the two units give different numbers, and find how much longer one thing is than another.
Using a ruler
A ruler is units laid end to end with numbers on them. Put one end of the object at 0. The number at the other end is its length.
If the object does not start at 0, count the units between its ends, or take the smaller number from the bigger one. A pencil from 2 to 11 is 11 − 2 = 9 centimeters long.
Inches and centimeters
An inch is about the length of the top part of a thumb. A centimeter is much smaller, about the width of a fingernail. Inches are used in the United States; centimeters are used in most of the world.
Because a centimeter is smaller, more of them fit. The same eraser is about 8 centimeters long: a bigger number for the same length.
How much longer
To find how much longer one thing is than another, measure both in the same unit and subtract.
Example: Comparing lengths
A rope is 34 centimeters long and a string is 19 centimeters long. How much longer is the rope?
- Both are in centimeters.
- 34 − 19 = 15.
Answer15 centimeters
Estimating first helps you check: a pencil is about 7 inches, a door about 80 inches.
Try it yourself
Work each one on paper first, then open the answer to check.
A key lies from 0 to 5 on an inch ruler. How long is it?
Show answer
5 inches.
A leaf lies from 3 to 10 on a centimeter ruler. How long is it?
Show answer
7 centimeters.
A book is 9 inches long. Will its length in centimeters be more or fewer than 9?
Show answer
More: centimeters are smaller, so more of them fit.
A blue ribbon is 48 cm and a red ribbon is 35 cm. How much longer is the blue one?
Show answer
13 cm.
Which is the better unit for a paper clip: inches or yards?
Show answer
Inches. A paper clip is about 1 inch long.