# Stage 3 – metric units

## Strategy

Students can:

• use a ruler and other measuring devices to measure lengths in metres, centimetres and millimetres
• record lengths in decimal notation

## Activities to support the strategy

1. Introduce key vocabulary for metric conversions of length. Write the following prefixes on the board:

milli thousandth of hundredth of 1000 wholes

Tell the students that these are prefixes used in the metric system when working with measurement. They tell us how much of something we have. The prefixes milli and centi tell us there is less than one whole.

• milli means a thousandth of
• centi means a hundredth of
• kilo means 1000 wholes. A kilometre equals 1000 metres

2. A basic procedure can be used to introduce each of the units of measurement and the process for converting units.

• Tell the function of the specific unit. For example, metres tell us how long something is. We use millimetres to measure objects that are not very big, centimetres to measure things that are medium sized and metres to measure objects which are big.
• Use concrete demonstrations of equivalencies in capacity, length and mass to illustrate each unit.
• Demonstrate how to use measuring tools, measuring to the nearest whole unit.
• Provide exercises which require students to determine the appropriate tool to use when measuring an object. Ask questions such as: What unit would we use to tell how long a pencil is? What unit would we use to measure how much juice we should give to the baby?
• Present equivalency facts, such as 10 millimetres equal one centimetre. This step should make links between units from all types of measures. Use an Equivalency Cue Card to support students while working on equivalency problems and to aid memory.
1000 millimetres = 1 metre ¼ metre 1 centimetre 1 metre ½ metre

3. Students work in pairs or small groups to find out the length of a piece of string.

Each group is given a ball of string or wool. Discuss strategies that could be used for finding out the total length, then use one of these strategies to determine the approximate length. Students record their measurement using the most appropriate units.

Each group reports back to the class and describes:

• the strategies they discussed which could be used to measure the length
• the process they used to measure the length
• what the actual length was and why they chose this unit to measure
• what other units could be used to record the length.

4. Record the lengths of string for each group on the board. Students in groups discuss how their length can be converted to a different unit. Challenge groups to identify as many ways as possible, using combinations of km, m, cm and mm. Ask each group to report back to the class and explain the different ways, e.g. if a group recorded the length as 157 metres, it could be written as 0.157 km, 15 700 cm, etc.

5. In a class discussion ask students to explain the relationship between the size of a unit and the number of units needed, e.g. more metres than kilometres will be needed to measure the same distance. Students explain how they would estimate 1 km using familiar objects.

• How many 50 m Olympic swimming pools placed end-to-end would make a distance of 1 km?
• How many desks placed end-to-end would make a distance of 1 km?

Students record measurements and their calculations.

## Resources

### Numeracy wrap

The long and the short – Students can measure objects of different length in centimetres and millimetres, order lengths from shortest to longest, convert between millimetres, centimetres, metres and kilometres.