Units and conversions · Grade 7
In Grade 7 you learn: area and volume units; converting compound units.
Metric units are built on 10, 100 and 1,000, so converting between them is just multiplying or dividing. Some countries also use imperial units like miles, pounds and gallons, which convert with approximate rates. Area and volume units need extra care.
Key facts
- Length: 10 mm = 1 cm, 100 cm = 1 m, 1,000 m = 1 km.
- Mass: 1,000 g = 1 kg, 1,000 kg = 1 tonne. Capacity: 1,000 ml = 1 litre.
- Big unit → small unit: multiply. Small unit → big unit: divide.
- Approximate imperial conversions: 5 miles ≈ 8 km, 1 inch ≈ 2.5 cm, 1 kg ≈ 2.2 pounds, 1 gallon ≈ 4.5 litres.
- Area: 1 m² = 100 × 100 = 10,000 cm². Volume: 1 m³ = 1,000,000 cm³.
- 1 cm³ = 1 ml, so 1,000 cm³ = 1 litre and 1 m³ = 1,000 litres.
Worked examples
Example 1
Change 3.5 m² into cm².
Answer: 35,000 cm²
Example 2
A fish tank measures 60 cm × 30 cm × 40 cm. How many litres does it hold when full?
Answer: 72 litres