ACARA v9 CONTENT DESCRIPTION “measure and compare objects using familiar metric units of length, mass and capacity, and instruments with labelled markings”
Knowing the units is only half of measuring; the other half is reading an instrument. Length comes from a ruler, mass from a scale, capacity from a measuring jug, and each of these tools carries labelled markings that turn a physical amount into a number you can write down and compare. This unit puts the three familiar quantities of Year 3 — length, mass and capacity — alongside the instruments that measure them, and practises both reading a single measurement and comparing two. Measuring well is a practical skill that runs through cooking, building, sport and shopping.
Read the ruler
An instrument with labelled markings lets you read a length exactly.
Read where the bar ends against the labelled marks. How long is it?
Reading length from a ruler
A ruler measures length by lining up one end of an object with zero and reading where the other end falls against the marks. The labelled marks — usually centimetres, with smaller millimetre lines between — are what make the reading exact rather than a guess. Lining the object up carefully at zero matters, because a measurement read from the wrong starting point is wrong by that much. Reading an instrument with labelled markings, exactly as the descriptor asks, is the heart of measuring length, and it is the same skill whether the ruler is in a pencil case or a tape measure on a wall.
Compare two lengths
Measuring both in the same unit lets you say which is longer.
Compare the two bars: is the top one longer, shorter, or the same as the bottom?
Comparing lengths fairly
Once two objects are measured in the same unit, comparing them is just comparing numbers: 15 cm is longer than 9 cm. The catch, and the reason units matter, is that a fair comparison needs the same unit for both — you cannot compare a length in centimetres with one in metres without converting first. Measuring both with the same ruler removes that trap entirely. Comparing measurements is how we answer real questions: which ribbon is longer, which path is shorter, whose tower is taller, and the answer is trustworthy only when the measuring was fair.
Read the scale
A kitchen scale's needle and labelled marks give the mass in grams.
Read where the needle points against the labelled marks. What is the mass?
Reading mass from a scale
A scale measures mass, and like a ruler it carries labelled markings — here the needle points to a number of grams. Reading it means finding where the needle sits and reading the nearest labelled mark, just as with length but around a dial. Small things are measured in grams and heavier things in kilograms, with a kilogram being a thousand grams. The instrument does the comparing for you indirectly: weigh two things and the numbers tell you which is heavier, without ever lifting them side by side.
Fill the jug
A measuring jug's labelled lines read capacity in millilitres.
Read the water level against the labelled mL lines. How much is in the jug?
Reading capacity from a jug
Capacity — how much a container holds — is measured with a jug whose side carries labelled lines in millilitres. Pour the liquid in, let it settle, and read the line the surface reaches. Small amounts are millilitres and larger amounts are litres, where a litre is a thousand millilitres, which is why a jug marked to 1000 mL is the same as one litre. Capacity completes the trio of Year 3 measures, and reading a jug works on exactly the same principle as the ruler and the scale: line up the amount with the labelled markings and read the number.
Pick the unit
Length, mass and capacity each have their own familiar metric units.
Which metric unit best measures the length of a pencil?
Choosing a sensible unit
Part of measuring well is choosing the right unit before you start. Length of a pencil in centimetres, length of a room in metres; mass of an apple in grams, mass of a child in kilograms; a drink in millilitres, a bath in litres. Picking a unit that suits the size of the thing keeps the numbers sensible — measuring a classroom in millimetres would give an enormous, awkward number. Matching unit to object is a quiet judgement that good measurers make automatically, and it is exactly the familiarity with metric units the curriculum is building.
Same family, compare
To compare two amounts, first express them in the same unit.
Which is bigger: 1 m or 80 cm? Put them in the same unit to be sure.
Comparing across units
Sometimes two amounts are given in different units of the same family, and to compare them fairly you must first put them in the same unit. Is 1 m longer than 80 cm? Convert the metre to 100 cm and the answer is clear. Is 2 kg heavier than 1500 g? Two kilograms is 2000 g, so yes. This converting-to-compare step joins the place-value thinking from Number to the measuring of this unit, and it rounds out a child's command of length, mass and capacity: name the unit, read the instrument, choose sensibly, and compare fairly. The next Measurement unit turns from these quantities to measuring time.
Quick self-check
1. A pencil lined up with a ruler ends at the 7 mark. How long is it?
2. Which unit best measures the mass of an apple?
3. A jug is filled to the 250 line marked in millilitres. The capacity is...
4. One string is 15 cm and another is 9 cm. The first string is...