Bigger to smaller, multiply: measures and units
The Short Answer
Your child knows there are a thousand grams in a kilogram. What the 11+ tests is applying that when there is a decimal point involved, and remembering to convert before comparing. Going from a bigger unit to a smaller one multiplies; from smaller to bigger divides. Make everything the same unit first, every time.
What do measures questions test?
Not the facts. Your child knows there are a thousand grams in a kilogram and a hundred centimetres in a metre.
What the paper tests is applying those facts when there is a decimal point in the way, and remembering to convert before comparing.
Which way round?
Bigger unit to smaller unit: multiply. Smaller unit to bigger unit: divide.
Worth saying the reason once, because a rule with a reason attached can be rebuilt when it is forgotten. A kilogram is a big unit, so it takes fewer of them to describe the same amount of stuff. Switch to grams — a small unit — and you need more of them, so the number gets bigger. Bigger number means multiply.
Same unit before comparing
Which is heavier, 0.4 kg or 350 g?
Compared as they stand, 350 is the bigger number and the wrong answer is tempting. Convert first — 0.4 kg is 400 g — and it takes no thought at all.
This applies to comparing, adding and subtracting alike. Make everything the same unit first, and choose whichever unit avoids decimals if you have the choice.
Can you show me a worked example?
The sensible-size check
A conversion error is almost never small. It is a factor of ten, a hundred or a thousand — so the wrong answer is not slightly off, it is ridiculous.
A person weighing 65 000 kg. A pencil 0.15 mm long. A journey of 4 cm.
Two seconds looking at the answer catches all of those, and nothing in the arithmetic will.
Where do pupils lose marks?
Comparing without converting, and picking the bigger number.
Multiplying when they should divide, usually with a decimal involved.
Converting at the end when the conversion belonged at the start.
Not looking at the answer to see whether it could be true.
Try it yourself
Ask which direction you are converting in before you calculate. Bigger to smaller multiplies.
- How many grams in 2.45 kg?
- How many litres is 1750 ml?
- Which is heavier: 0.4 kg or 350 g?
- A plank is 1.2 m long. How many 15 cm pieces can be cut from it?
- Why is checking the size of the answer worth two seconds?
- 2450 g. Kilograms to grams is bigger to smaller, so multiply by a thousand. The decimal makes it feel harder and changes nothing about the direction.
- 1.75 litres. Millilitres to litres is smaller to bigger, so divide by a thousand.
- 0.4 kg. Convert first — 0.4 kg is 400 g — and then it is obvious. Comparing 0.4 with 350 without converting invites the answer that 350 is larger, since it is a larger number.
- 8. Convert the plank to centimetres: 1.2 m is 120 cm. Then 120 ÷ 15 = 8. The conversion is the first step, not the last.
- Because a conversion error is almost always a factor of ten, a hundred or a thousand — so the wrong answer is wildly the wrong size. A person weighing 65 000 kg or a pencil 0.15 mm long announces itself instantly, if you look.
How much practice does this type need at home?
Kitchen scales and a measuring jug. Ask for 250 g of something and then ask what that is in kilograms. Fill a jug to 750 ml and ask for it in litres.
The number and the thing are in front of them at the same time, which is what makes the conversion stick — and it is considerably more convincing than a page of arrows between units.
Free: a Maths workbook
Questions across the Maths question types, with the method printed at the top and full answers at the back. One workbook for the whole strand, not a sheet per question type.
Frequently Asked Questions
Which way round do multiplying and dividing go?
Bigger unit to smaller unit, multiply. Smaller to bigger, divide. The reason is worth saying once: a kilogram is a big unit, so it takes fewer of them to describe the same amount — meaning the number gets larger when you switch to grams. Children who learn the rule with the reason attached recover it when they forget; children who learn it as a rule guess when they forget.
Why does my child get conversions wrong when they know the facts?
Because the decimal point is doing the damage rather than the fact. 2.45 kg to grams is the same conversion as 2 kg to grams, and it feels different. It helps to do the easy version first — 2 kg is 2000 g — and then place the harder one beside it, since the answer must be a little more.
When does the conversion come first?
Whenever the question names a unit the numbers are not written in. If a plank is given in metres and the pieces in centimetres, converting is step one and everything else follows. Children frequently do the division first and convert the answer afterwards, which sometimes works and often does not.
What is the sensible-size check?
Look at your answer and ask whether it could be true. A conversion error is nearly always a factor of ten or a hundred, so the wrong answer is not slightly wrong — it is absurd. A door 2000 m high, a bag of sugar weighing 1 g. It takes two seconds and catches the errors that the arithmetic never will.
Sources
- GL Assessment — 11+ familiarisation materials and question type descriptions Published 2025.
- Clever Clogs Academy — our own Year 4 and Year 5 lesson records, Winslow Published September 2025 to July 2026.
We are not affiliated with, endorsed by or connected to GL Assessment or Buckinghamshire Council. Test arrangements change; always check the council's own pages for the current year's dates.
We Teach This Method Every Week in Winslow
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