Metric Units of Length
Metric units of length use a base-10 system centered on the meter in Grade 8 math (Yoshiwara Core Math, Chapter 3). Key units: 1 kilometer (km) = 1,000 meters; 1 meter = 100 centimeters (cm); 1 cm = 10 millimeters (mm). Conversions involve shifting the decimal point: 2.5 km = 2,500 m. The metric system is the international scientific standard used globally. Converting metric lengths is simpler than English units because all conversions are powers of 10.
Key Concepts
Property Metric Units of Length: $$1 \text{ centimeter} = 10 \text{ millimeters}$$ $$1 \text{ meter} = 100 \text{ centimeters}$$ $$1 \text{ kilometer} = 1000 \text{ meters}$$ The conversion factors in the metric system are all powers of 10. This property makes the metric system easy to use, because we can convert between units simply by moving the decimal point.
Examples A table is 2.5 meters long. To convert this to centimeters, you move the decimal two places to the right: $2.5 \text{ m} = 250 \text{ cm}$.
A small insect measures 6 millimeters long. In centimeters, this is $6 \div 10 = 0.6$ centimeters.
Common Questions
What are the main metric length units?
Millimeter (mm), centimeter (cm), meter (m), kilometer (km). The meter is the base unit.
How many centimeters are in a meter?
100 cm = 1 m.
How do you convert 3.2 km to meters?
Multiply by 1,000: 3.2 × 1,000 = 3,200 m.
How do you convert centimeters to millimeters?
Multiply by 10. For example, 5.4 cm = 54 mm.
Why is the metric system easier for conversions?
All conversions are powers of 10 — just move the decimal point. English units require memorizing irregular factors like 5,280 ft/mile.
How many mm in a km?
1,000,000 mm (1 km = 1,000 m; 1 m = 1,000 mm → 10⁶).