Why round?
Sometimes an exact number is more detail than we need. "About 50 people came" is easier to remember than "47 people came". Rounding replaces a number with a nearby, friendlier one, usually ending in zeros.
Rounding on a number line
To round 47 to the nearest ten, find the tens on either side: 40 and 50.
40 — 41 — 42 — 43 — 44 — 45 — 46 — 47 — 48 — 49 — 50
47 is closer to 50, so 47 rounds to 50.
The number 45 is exactly halfway. By agreement, halfway numbers round up, so 45 rounds to 50.
The rounding rule
- Find the rounding digit: the digit in the place you’re rounding to.
- Look at the digit just to its right.
- If that digit is 5 or more, round up: add 1 to the rounding digit.
- If it is 4 or less, round down: keep the rounding digit.
- Change every digit to the right of the rounding digit to 0.
Examples in a table
| Number | Round to | Rounding digit | Digit to the right | Result |
|---|---|---|---|---|
| 47 | nearest 10 | 4 (tens) | 7 → up | 50 |
| 312 | nearest 10 | 1 (tens) | 2 → down | 310 |
| 365 | nearest hundred | 3 (hundreds) | 6 → up | 400 |
| 1,248 | nearest hundred | 2 (hundreds) | 4 → down | 1,200 |
| 7,500 | nearest thousand | 7 (thousands) | 5 → up | 8,000 |
Rounding with a 9
When the rounding digit is 9 and you round up, it becomes 10, so you carry 1 to the next place:
- 296 to the nearest ten: the tens digit is 9, next digit 6 → round up. 290 + 10 = 300.
- 9,970 to the nearest hundred: hundreds digit 9, next digit 7 → 10,000.
When we round
- Estimating answers before you calculate.
- Reporting crowd sizes or distances ("about 300 km").
- Money: rounding $19.95 to about $20.
Worked examples
Example 1: Round 47 to the nearest ten.
Tens digit 4, next digit 7 (5 or more) → 50.
Example 2: Round 832 to the nearest hundred.
Hundreds digit 8, next digit 3 → round down → 800.
Example 3: Round 4,651 to the nearest thousand.
Thousands digit 4, next digit 6 → 5,000.
Common mistakes
- Rounding up every time. Only round up when the next digit is 5 or more.
- Looking at the wrong digit. Always check the digit just right of the rounding place.
- Forgetting the zeros: rounding 365 to the nearest hundred and writing "4".
- Rounding in steps (365 → 370 → 400). It happens to work here, but 349 → 350 → 400 is wrong; 349 rounds to 300. Always round directly from the original number.
Try it yourself
- Round 63 to the nearest ten.
- Round 85 to the nearest ten.
- Round 449 to the nearest hundred.
- Round 2,950 to the nearest hundred.
- Round 15,499 to the nearest thousand.
Answers: 1) 60 2) 90 3) 400 4) 3,000 5) 15,000
Quick recap
- Look at the digit to the right of the rounding digit.
- 5 or more → round up; 4 or less → round down.
- Fill the places to the right with zeros, and round from the original number.