Measuring Line Segments
Learn how to measure, compare, and calculate with line segments like a geometry expert!
Units of Length
Metric Units and Conversions
Key Conversions to Remember:
- 1 kilometer (km) = 1,000 meters (m)
- 1 meter (m) = 100 centimeters (cm) = 1,000 millimeters (mm)
- 1 centimeter (cm) = 10 millimeters (mm)
Larger → Smaller: MULTIPLY
Example: 3 m 25 cm = (3 × 100) + 25 = 325 cm
Smaller → Larger: DIVIDE
Example: 450 mm = 450 ÷ 10 = 45 cm
Choosing the Right Unit
Interactive visualization — available in the full lesson
| Unit | Best For | Examples |
|---|---|---|
| mm | Tiny objects | Paper thickness, ant |
| cm | Everyday objects | Pencil, book, hand |
| m | Large objects | Room, person, car |
| km | Long distances | Between cities, roads |
Measuring with a Ruler
How to Measure Correctly
- Align the ZERO mark with one endpoint of the segment
- Read the number where the other endpoint falls
- Record with the correct unit (cm or mm)
What if you don't start at zero?
Length = End number − Start number
Example: Start at 2 cm, end at 9 cm → Length = 9 − 2 = 7 cm
Notation
The length of segment AB is written as AB (without a line over it)
Example: AB = 7 cm means "segment AB has length 7 centimeters"
Interactive Ruler
Interactive visualization — available in the full lesson
Drag point B to measure different lengths!