How do you 'convert into the same units'?
Children learn about measuring weight, capacity (volume of liquid) and length throughout their time at primary school.
In Year 1 they use non-standard units to compare measurements, such as measuring length with their hand spans, weighing objects on a balance in comparison to piles of blocks or using a certain cup to measure how many cupfuls of water make up the capacity of another container.
In Year 2 children start to use standard units, so grams and kilograms for weight, millilitres and litres for capacity and metres and centimetres for length.
In Year 3 children need to understand the relationship between units of measurement, so they need to know the following:
The knowledge then prepares them for being able to convert between units of measurement in Year 4 and Year 5, so if they are given the following measurements: 1400g, 600ml and 150cm they would know how to convert these into 1.4kg, 0.6 litres and 1.5m.
Coverting between units of measurement in KS2
Children in upper Key Stage 2 will often need to solve word problems involving measures that require them to convert one measurement so that both measurements are in the same unit, for example:
I am 1.2m tall. My sister is 85 cm tall. How much taller am I than my sister?
Usually, a child would convert 1.2m to 120 cm and then would easily be able to work out that the difference between 85cm and 120cm (which is 35cm).
In Year 6, children need to convert between units using decimals to three places, so they may come across a problem like the following:
I have 2.45 litres of orange juice. I pour 500ml of orange juice out and drink it. How much do I have left?
To work this out, it is likely a child would need to convert 2.45 litres to 2450ml, then subtract 500ml from this to make 1950ml.
In Year 6 children might also be asked to convert between imperial and metric units of measurement.
Children need a lot of practice with converting units of measurement. There can be some confusion over the fact that grams and millilitres deal in thousands and centimetres deal in hundreds. It is a really good idea for children to become confident with how many millilitres, grams and centimetres are in a litre, kilogram and metre in Year 4. (This may need lots of testing, little and often!)