11 plus Units & Conversion questions

What a Units & Conversion question looks like

Units & Conversion is the 11 plus measurement topic that asks a child to write the same measurement a different way. A weight given in grams has to come out in kilograms, a running track measured in metres has to come out in kilometres, a jug marked in litres has to be counted in millilitres. The measurement never changes, only the unit it is written in.

That is worth holding on to, because measurement has several near neighbours: Units & Conversion changes the unit, where Perimeter, Area & Volume measures the shape itself, Money works in a single step of a hundred, and Time carries at 60 minutes rather than at 10, 100 or 1,000. Almost every question here moves up or down the metric ladder by multiplying or dividing by 10, 100 or 1,000, and where one needs another factor, such as centilitres or an inch given as 2.5 cm, the question states it.

They are not all bare conversions. Some ask for a total or a difference first and convert at the end, some bury the conversion inside a longer problem about tiles, planks or bags of flour, and some carry a table, a bar chart, a line graph or a pictogram measured in one unit and ask the question in another. Of the five answer options, four typically hold the right digits with the decimal point in the wrong place.

Example one: do the sum, then convert

Ava has 5 boxes. Each box weighs 800 g. What is the total weight in kilograms?

Weigh before you convert. Five boxes at 800 g each is 5 × 800 = 4000 g. Now change grams into kilograms: there are 1000 g in 1 kg, so 4000 ÷ 1000 = 4 kg. Check it backwards, because 4 × 1000 = 4000 g is where we started.

The answer is 4 kg.

The tempting wrong option is 4000 kg. A child who multiplies well and then stops has the right digits already, and copies the unit straight from the question. Two more options, 400 kg and 40 kg, come from dividing by 10 or 100 when the step needed 1000.

Example two: a table in one unit, a question in another

Some questions carry a small table of measurements and ask about a unit the table does not use. This one gives four containers:

Which container holds exactly 1.5 litres?

Convert the question, not the whole table. The capacities are in millilitres, so turn 1.5 litres into millilitres and look for it: one litre is 1000 ml, so 1.5 × 1000 = 1500 ml. Container Y holds 1500 ml.

The answer is Container Y.

Container X catches a child who multiplies by 10,000 rather than 1000, since 15000 ml is 15 litres, ten times too much. Container Z, 1050 ml, catches a child who reads 1.5 litres as one thousand and fifty millilitres. Converting the one number in the question beats converting four in the table.

Example three: the conversion in the middle

A plank of wood is 3.6 m long. It is cut into pieces each 45 cm long. How many complete pieces can be cut?

Two lengths in two different units cannot be divided until they match. Metres to centimetres is a step of 100, so 3.6 m = 360 cm. The division is then straightforward: 360 ÷ 45 = 8. Check backwards again, because 8 pieces of 45 cm make 360 cm.

The answer is 8 complete pieces.

The trap option is 80, and it comes from a sensible decision carried out on half the question. A child who turns the plank into millimetres gets 3600 mm, which is right, then divides by 45 without also turning 45 cm into 450 mm. Convert both measurements or neither.

How to answer it

1. Read to the end and underline the unit the answer has to be given in. The wrong options are built around that unit.
2. If two of the measurements are in different units, change one so they match before you add, subtract, multiply or divide. If they already match, do the arithmetic first and convert once at the end.
3. Choose the step: 10 between millimetres and centimetres, 100 between centimetres and metres, and 1000 between metres and kilometres, between grams and kilograms, and between millilitres and litres.
4. Decide between multiplying and dividing by asking whether the number should get bigger or smaller. A smaller unit means you need more of them, so kilograms into grams makes the number bigger.
5. Convert your answer back the other way as a check. If it does not land on the number the question started with, the decimal point has moved the wrong distance.

Common mistakes

• Right number, wrong unit. The most common lost mark is a correct calculation labelled with the unit from the question rather than the one asked for: 4000 kg for 4 kg, 900 m for 9 m.
• Moving the decimal point the wrong distance. Dividing by 10 or 100 where the step was 1000 turns 4 kg into 400 kg or 40 kg. Most of the wrong options are one of these, which is why they all look reasonable.
• Converting one measurement and forgetting the other. A plank in millimetres divided by pieces in centimetres gives an answer ten times too big, and nothing looks wrong on the page.
• Stopping one step early. Turning 4500 ml into 4.5 litres and forgetting to add the extra 1.5 litres. The conversion feels like the answer because it was the hard part.
• Converting a whole table instead of the question. When a table, chart or pictogram uses a different unit, one conversion is needed, not five.

How to practise 11 plus Units & Conversion questions

Short and frequent beats long and occasional here, because what a child is building is the reflex of checking the unit before writing the answer down. When your child gets one wrong, resist explaining it and ask them to convert their answer back the other way instead: nine times out of ten they find the misplaced decimal point themselves, and finding it is what makes it stick. Kitchen scales and a measuring jug help too, early in eleven plus maths preparation, because they make grams, kilograms, millilitres and litres real rather than abstract. 11+ Daily has a Units & Conversion project alongside the rest of the measurement work, on laptop, tablet or phone, and the full list sits on our 11 plus maths practice page. How often to sit down to it is covered in how much 11 plus practice a child needs each day. Every question is original to 11+ Daily, nothing is a past paper and nothing is licensed from another publisher, and the bank is re-checked in rounds.

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