Length, Mass and Capacity
Measuring needs the right tool
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.
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.
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.
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.
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.
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.
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.