Rounding to the nearest ten
Rounding a number means replacing it with a simpler number that's very close to it. The rule is always the same: look at the digit right after the position you're rounding to.
- Find the units digit (the one that's going to disappear).
- If it's 0, 1, 2, 3 or 4, round down (keep the tens digit, put a 0 in the units place).
- If it's 5, 6, 7, 8 or 9, round up (add 1 to the tens digit, put a 0 in the units place).
43 → 40 · 47 → 50 · 45 → 50
3 and 4 round down; 5, 6, 7 round up
Rounding to the nearest hundred and thousand
The principle is exactly the same, you just shift your focus one position along. To round to the nearest hundred, look at the tens digit. To round to the nearest thousand, look at the hundreds digit.
- 367 to the nearest hundred → the tens digit is 6 (≥5) → 400.
- 2,340 to the nearest thousand → the hundreds digit is 3 (<5) → 2,000.
- 6,800 to the nearest thousand → the hundreds digit is 8 (≥5) → 7,000.
It links directly to the place-value chart: rounding "wipes out" the digits after the chosen position and replaces them with 0s, only adjusting the digit just before if needed.
Why estimate before calculating?
Estimating means using rounded numbers, easy to work with in your head, to quickly guess an approximate result — before doing the exact calculation. It's used afterwards to check the result found makes sense: if the estimate gives "about 500" and the exact calculation gives 5,040, there's probably a mistake (a misplaced decimal point, a missed digit).
Estimating a sum or a difference
Round each number to the same place value (tens, hundreds…), then calculate with the rounded numbers, which are much simpler.
387 + 512 ≈ 400 + 500 = 900
Exact result: 899 — the estimate is very close!
For a difference: 592 − 208 ≈ 600 − 200 = 400 (exact result: 384).
Estimating a product or a quotient
For a multiplication, round each factor, often to the nearest ten or hundred, to get back to a times table you already know.
29 × 41 ≈ 30 × 40 = 1,200
Exact result: 1,189 — the estimate confirms the order of magnitude
For a division, look for a nearby number that divides easily: 238 ÷ 6 ≈ 240 ÷ 6 = 40 (exact result: about 39.7).
Estimating with decimal numbers
The same method applies to decimal numbers: round each one to the nearest whole number or ten before estimating.
7.8 + 4.3 ≈ 8 + 4 = 12
Exact result: 12.1 — the estimate helps check you haven't misplaced the decimal point
Mistakes to avoid
- Forgetting the rule "5 always rounds up", and rounding 45 down to 40.
- Looking at the wrong digit: to round to the hundred, you need to look at the tens digit, not the units.
- Thinking an estimate must be exact — it's only there to check the order of magnitude, not to replace the precise calculation.
- Rounding the two numbers to different place values within the same estimate (one to the nearest ten, the other to the nearest hundred).
Worked exercises
Round 683 to the nearest ten
Round 3,458 to the nearest hundred
Estimate 198 + 305 by rounding to the nearest hundred
Estimate 21 × 39 by rounding to the nearest ten
Now it's your turn!
On EasyMaths, your child practises rounding and estimating with exercises that never repeat and instant marking.
Start the exercises →Frequently asked questions
How do you round a number to the nearest ten?
Look at the units digit. If it's less than 5 (0 to 4), round down by putting a 0 in the units place. If it's 5 or more (5 to 9), round up. Example: 43 becomes 40, 47 becomes 50.
Why estimate a result before calculating?
Estimating lets you check that the exact result you got is reasonable, and spot a big calculation mistake (a misplaced decimal point, a missed digit). It's a habit used all through life, at the shops or at work, long before reaching for a calculator.
What's the difference between rounding and estimating?
Rounding means replacing one number with a simpler nearby number (47 becomes 50). Estimating means using rounded numbers to quickly work out an approximate result for a calculation, before or instead of the exact calculation.