3.472
3 = three ones
4 = four tenths (4/10)
7 = seven hundredths (7/100)
2 = two thousandths (2/1000)
KS2 Decimals — Year 6 Guide with Examples
Decimals pop up everywhere in Year 6 SATs — on the arithmetic paper, in reasoning word problems, and even in measurement questions. Once your child understands that decimals are just another way of writing fractions, everything becomes much less daunting.
Decimal Place Value
In a decimal number, every digit has a value based on its position. To the left of the decimal point we have ones, tens, hundreds — the familiar stuff. To the right, we have tenths, hundredths and thousandths.
A good way to remember it: on the left the columns get ten times bigger; on the right they get ten times smaller. Same pattern, just mirrored around the decimal point.
Ordering Decimals
When comparing decimals, start at the left and work your way right, one column at a time — exactly the same as comparing whole numbers.
Put in order, smallest first: 0.45, 0.405, 0.5, 0.41
Line them up: 0.450, 0.405, 0.500, 0.410
Answer: 0.405, 0.41, 0.45, 0.5
Top tip: padding with trailing zeros (so every number has the same number of decimal places) makes it much easier. 0.5 becomes 0.500 — now the comparison is obvious.
Adding and Subtracting Decimals
The golden rule: line up the decimal points. Once they’re aligned, it works exactly like normal column addition or subtraction.
12.65
+ 3.8 ← think of it as 3.80
-------
16.45
If one number has fewer decimal places, pad it with a trailing zero. This stops children accidentally putting digits in the wrong column.
Multiplying and Dividing by 10, 100 and 1000
This is one of the most common SATs questions and one of the easiest to get right with the correct method. Every digit moves left (for multiplying) or right (for dividing).
3.45 × 10 = 34.5 (digits shift one place left)
3.45 × 100 = 345 (digits shift two places left)
3.45 ÷ 10 = 0.345 (digits shift one place right)
3.45 ÷ 100 = 0.0345 (digits shift two places right)
Never say “move the decimal point”. The decimal point stays put — it’s the digits that move. This avoids all sorts of confusion.
Rounding Decimals
Rounding works the same way as with whole numbers. Look at the digit after the place you’re rounding to. If it’s 5 or more, round up. If it’s 4 or less, round down.
Round 3.472 to one decimal place:
Look at the hundredths digit: 7 (5 or more → round up)
Answer: 3.5
Round 6.849 to two decimal places:
Look at the thousandths digit: 9 (5 or more → round up)
Answer: 6.85
SATs-Style Example Question
“A piece of rope is 4.2 metres long. Sam cuts off 1.85 metres. How much rope is left?”
4.20
− 1.85
------
2.35 metres
Notice how we wrote 4.2 as 4.20 — padding with a zero makes the subtraction straightforward and avoids column-alignment errors.
Common Mistakes to Watch For
- Thinking 0.45 is bigger than 0.5 — because 45 is bigger than 5. Padding with zeros (0.45 vs 0.50) fixes this instantly.
- Moving the decimal point instead of the digits — this leads to errors when multiplying or dividing by 10, 100, 1000.
- Forgetting to line up decimal points — in column addition or subtraction, one misaligned column ruins the whole calculation.
- Rounding too early — in multi-step problems, only round the final answer, not the intermediate steps.
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