Ross MackellUK-qualified primary teacher · 9 min read

Round 2,961 to the nearest hundred. A lot of children write 2,1000. Others write 2,900. The answer is 3,000, and the reason so many children get stuck is that nobody showed them what rounding actually means.

Rounding is one of those skills that looks small but turns up everywhere: estimating answers, checking calculations, money, measurements, and a steady stream of SATs questions. It's also the skill that tells you most quickly whether your child really understands place value.

I'm Ross, a UK-qualified primary teacher with over ten years in the classroom. In this guide I'll show you the one rule behind all rounding, the number line picture that makes it click, how to round decimals, how to use rounding to estimate, the mistakes I see most often, and practice questions with answers.

What your child needs first

Rounding is built on one skill:

• Place value. Your child needs to know what each digit in a number is worth. If they can't tell you that the 4 in 347 means 40, rounding will always feel like a trick to memorise. See what is place value.
• Counting in 10s, 100s and 1,000s. To round 347 to the nearest 10, your child needs to know that it sits between 340 and 350.

In the national curriculum, children round to the nearest 10, 100 and 1,000 in Year 4, along with rounding decimals with one decimal place to the nearest whole number. In Year 5 they round numbers up to 1,000,000 and decimals with two decimal places. In Year 6 they round to any required degree of accuracy and use rounding to solve problems.

What rounding actually means

Rounding means finding the nearest "friendly" number. Before any rules, draw a number line. Here's 347 between 340 and 350:

347 is past the halfway point of 345, so it's closer to 350. That's all rounding is. The rule your child learns later is just a shortcut for spotting which side of halfway a number sits on.

The only tricky case is a number exactly on halfway, like 345. The rule we use in schools is that halfway always rounds up, so 345 rounds to 350.

The rounding rule, step by step

Example 1: round 347 to the nearest 10

1. Find the tens digit. In 347, it's the 4.
2. Look at the digit to its right, the ones digit: 7.
3. 7 is 5 or more, so round up. The 4 becomes a 5.
4. Every digit after it becomes zero. The answer is 350.

Example 2: round 832 to the nearest 10

1. The tens digit is 3.
2. The digit to its right is 2.
3. 2 is 4 or less, so round down. The 3 stays as a 3.
4. The ones become zero. The answer is 830.

Notice that "round down" doesn't mean the tens digit goes down. It stays the same. That catches a lot of children out (see mistake 2 below).

A rhyme some schools use: "5 or more, raise the score. 4 or less, let it rest."

Rounding to 100, 1,000 and beyond

The rule never changes. Only the digit you look at changes.

That last row is a fun one to show your child. To the nearest 100,000, 46,582 is closer to 0 than to 100,000, so it rounds to 0. It proves rounding is about which number is closest, not about following steps blindly.

Example 3: the tricky 9s

Round 2,961 to the nearest 100. The hundreds digit is 9 and the digit to its right is 6, so we round up. But 9 can't become 10 in one column. Instead, think about the number line: 2,961 sits between 2,900 and 3,000, and it's closer to 3,000. The 9 rolls over into the thousands, just like 2,900 + 100 = 3,000.

Rounding decimals

Decimals follow exactly the same rule. If decimals feel shaky, adding and subtracting decimals is a useful refresher on what each digit means.

Example 4: round 3.47 to the nearest whole number

1. The ones digit is 3.
2. Look at the digit to its right, the tenths digit: 4.
3. 4 is 4 or less, so round down. The answer is 3.

Example 5: round 3.47 to one decimal place

1. One decimal place means rounding to the tenths. The tenths digit is 4.
2. Look at the digit to its right, the hundredths digit: 7.
3. 7 is 5 or more, so round up. The 4 becomes a 5. The answer is 3.5.

With decimals, the digits after the one you're rounding to are dropped rather than turned into zeros. 3.47 to one decimal place is 3.5, not 3.50.

Example 6: round 6.95 to one decimal place

The tenths digit is 9 and the digit after it is 5, so round up. The 9 rolls over, just like the tricky 9s above, and 6.95 becomes 7.0. Keep the zero: writing 7.0 shows the answer has been rounded to one decimal place.

Using rounding to estimate

This is where rounding earns its keep. Before your child works out a calculation, rounding each number gives them a rough answer to check against.

• 49 × 21 is roughly 50 × 20 = 1,000. The real answer is 1,029, so that looks right.
• 612 − 287 is roughly 600 − 300 = 300. The real answer is 325.
• £4.95 + £3.10 is roughly £5 + £3 = £8.

If your child does a long multiplication and gets 10,290 for 49 × 21, a quick estimate tells them straight away that something's gone wrong. It's one of the best habits you can build at home.

5 common mistakes and how to fix them

Mistake 1: Looking at the wrong digit

Rounding 347 to the nearest 10, your child looks at the 4 and rounds down to 340.

The fix: underline the digit you're rounding to, then point to the one next door on the right. That's the only digit that decides.

Mistake 2: Making the digit go down when rounding down

Your child rounds 832 to the nearest 10 and writes 820.

The fix: go back to the number line. 832 is between 830 and 840. 820 isn't even one of the options. Rounding down means the digit stays the same.

Mistake 3: Forgetting the zeros

Your child rounds 4,682 to the nearest 1,000 and writes 5.

The fix: ask "is 4,682 about 5, or about 5,000?" The zeros hold the place value. Without them the number is a thousand times too small.

Mistake 4: Rounding in a chain

To round 3.45 to the nearest whole number, your child first rounds to 3.5, then rounds 3.5 up to 4.

The fix: always round from the original number, in one step. 3.45 is closer to 3 than to 4, so the answer is 3.

Mistake 5: Getting stuck on 9s

Rounding 2,961 to the nearest 100, your child writes 2,1000.

The fix: ask "which two hundreds is it between?" Once they say 2,900 and 3,000, the answer is obvious.

Practice questions

Same three steps I use for every skill: watch, copy, practise. Do the first one out loud yourself, then let your child have a go at a similar one before they try the rest on their own. Cover the last column and ask your child to fill in the gaps.

Bonus question: a number rounds to 400 when rounded to the nearest 10. What's the smallest whole number it could be, and the largest? (Answer: smallest 395, largest 404.)

Ten minutes, a few times a week, is plenty. Only move on when they're getting three in a row right.

Frequently asked questions

How do you round to the nearest 10?

Look at the ones digit. If it's 5 or more, round the tens up. If it's 4 or less, keep the tens the same. The ones digit becomes zero. So 67 rounds to 70, and 64 rounds to 60.

Does 5 round up or down?

In UK primary schools, 5 always rounds up. So 45 rounds to 50 to the nearest 10, and 2.5 rounds to 3 to the nearest whole number.

How do you round to one decimal place?

Look at the hundredths digit, the second digit after the decimal point. If it's 5 or more, round the tenths digit up. If it's 4 or less, keep it the same. Then drop the digits after it. So 3.47 rounds to 3.5.

Why do children learn rounding?

Rounding helps children estimate answers and check whether their calculations make sense. It's also used with money, measurements and data, and it appears regularly in KS2 SATs questions.

What year do children learn rounding?

In England, children round to the nearest 10, 100 and 1,000 in Year 4. In Year 5 they round numbers up to 1,000,000 and decimals to one decimal place. In Year 6 they round to any degree of accuracy and use rounding to solve problems.

Sources and further reading

• Department for Education, National curriculum in England: mathematics programmes of study (number and place value, Years 4, 5 and 6)
• Standards and Testing Agency, Key stage 2 mathematics test framework
• Ross Mackell, Teacher's Perspective on YouTube