Metric units (Edexcel GCSE Maths): Revision Notes
Metric units
What are metric units?
Metric units are standardised measurements used for length, weight, and volume. The metric system makes conversions simple because all units are related by factors of 10, 100, or 1000.
You can convert between metric units by multiplying or dividing by these key numbers: 10, 100, or 1000.
The beauty of the metric system lies in its decimal-based structure, making it much easier to work with than imperial systems that use irregular conversion factors.
Types of metric units
Length
The main units for measuring length are:
- Kilometres (km) - for long distances
- Metres (m) - for medium distances
- Centimetres (cm) - for shorter measurements
- Millimetres (mm) - for very small measurements
Length Conversion Factors:
Weight
The main units for measuring weight are:
- Tonnes - for very heavy objects
- Kilograms (kg) - for everyday weights
- Grams (g) - for lighter items
- Milligrams (mg) - for very light measurements
Weight Conversion Factors:
Volume or capacity
The main units for measuring volume are:
- Litres - for larger volumes
- Centilitres (cl) - for medium volumes
- Millilitres (ml) - for smaller volumes
- Cubic centimetres (cm³) - equivalent to ml
Volume Conversion Factors:
Using place value diagrams for conversions
Place value diagrams help you multiply and divide by 10, 100, and 1000 correctly by showing how digits move between positions.
To multiply by 10, 100, or 1000: Move the digits 1, 2, or 3 places to the left respectively.
To divide by 10, 100, or 1000: Move the digits 1, 2, or 3 places to the right respectively.
Multiplication examples: , ,
Division examples: , ,
Worked example
Worked Example: Finding the Weight of Paper
Problem: A ream of paper weighs 2.5 kg and contains 500 sheets. What is the weight of one sheet in grammes?
Step 1: Convert kg to g
Step 2: Divide by number of sheets
Answer: Each sheet weighs 5 grammes.
Common exam mistakes
The examiner's report highlights that students frequently lose marks by converting between different metric units incorrectly.
Key tip: Always check your conversion makes sense. When converting to a smaller unit (like kg to g), your number should get bigger. When converting to a larger unit (like g to kg), your number should get smaller.
Example: ✓ (The number got bigger because grammes are smaller units)
Remember!
Key Points to Remember:
- Metric conversions use factors of 10, 100, or 1000
- Moving left in place value = multiplying (number gets bigger)
- Moving right in place value = dividing (number gets smaller)
- Always check your answer makes logical sense
- Smaller units give bigger numbers, larger units give smaller numbers