Rounding Decimals – To Any Decimal Place
Rounding a decimal means replacing it with a simpler number that is close in value. You round when an exact decimal would be too long or more precision than you need.
Why Round?
- A calculator gives 6.3478245 as an answer — you only need 6.35.
- A petrol price of 152.9p per litre is really 153p to the nearest penny.
- A measurement of 3.14159... is written as 3.14 for most purposes.
The Basic Rule
Look at the digit one place to the right of where you are rounding.
If it is 5 or more — round up (increase the rounding digit by 1).
If it is 4 or less — round down (keep the rounding digit the same).
Drop all digits after the rounding position.
Rounding to the Nearest Whole Number
Tenths digit is 3 (less than 5). Round down. Answer: 7.
Tenths digit is 8 (5 or more). Round up. Answer: 5.
Rounding to One Decimal Place
Hundredths digit is 7 (5 or more). Round up the tenths digit: 4 becomes 5. Answer: 3.5.
Hundredths digit is 2 (less than 5). Round down. Answer: 8.4.
Rounding to Two Decimal Places
Thousandths digit is 8 (5 or more). Round up the hundredths digit: 7 becomes 8. Answer: 5.68.
Thousandths digit is 4 (less than 5). Round down. Answer: 12.30.
Carrying When Rounding Up
Hundredths digit is 7. Round up tenths digit: 9 becomes 10. Carry: the whole number becomes 10. Answer: 10.0.
Summary Table
| Number | Nearest Whole | 1 d.p. | 2 d.p. |
|---|---|---|---|
| 3.456 | 3 | 3.5 | 3.46 |
| 7.995 | 8 | 8.0 | 8.00 |
| 0.074 | 0 | 0.1 | 0.07 |
Key Takeaways
- Always look one place beyond where you are rounding.
- 5 or above — round up; 4 or below — round down.
- Remember to carry if rounding up creates a 10.
- Keep trailing zeros when specified (e.g., 3.50 not 3.5 when rounding to 2 d.p.).
Practice Questions
- Round 6.38 to the nearest whole number.
- Round 4.753 to 1 decimal place.
- Round 0.0456 to 2 decimal places.
- A length is measured as 12.849 m. Round to the nearest tenth of a metre.
- Round 2.995 to 2 decimal places (watch for the carry).