Rounding decimals (age 9+)
Round decimals with two decimal places to the nearest whole number and to one decimal place
What a learner can do afterwards
- Round 3.47 to the nearest whole number (3) and to 1 d.p. (3.5)
- Round 12.95 to 1 d.p. (13.0) and explain the boundary case
- Estimate 4.83 + 2.17 by rounding each to the nearest whole number
1 · Read
To round a decimal to the nearest whole number, look at the tenths digit. That is the first digit after the decimal point. If it is 5 or more, round up. If it is less than 5, keep the whole number the same.
3.47 has a 4 in the tenths place. Four is less than five, so 3.47 rounds down to 3.
Rounding to one decimal place works the same way, but you check one digit further: the hundredths digit. That is the second digit after the point.
When you estimate a sum, round each decimal to the nearest whole number first, then add. 4.83 rounds to 5, and 2.17 rounds to 2, so the estimate is 5 + 2 = 7.
Check the digit right after the place you are rounding to: 5 or more rounds up, below 5 stays the same.
More to read
Decimals and how to round them
A decimal number has two parts. The part before the decimal point is the whole number part, like the 3 in 3.47. The part after the point tells about tenths and hundredths. In 3.47, the 4 means 4 tenths and the 7 means 7 hundredths.
Rounding a decimal means finding the closest simpler number. To round 3.47 to the nearest whole number, look at the tenths digit. It is 4, which is less than 5, so the number stays at 3. To round 3.47 to one decimal place, look at the hundredths digit. It is 7, which is 5 or more, so 3.4 rounds up to 3.5.
Find the place you are rounding to, look one digit to the right, and if that digit is 5 or more, round up. Otherwise, keep the digit the same.
Watch out for carry overs. When you round 12.95 to one decimal place, the tenths digit is 9 and the next digit is 5, so it rounds up. Nine tenths plus one more tenth makes a whole new one, and the answer is 13.0.
Rounding is also a superpower for estimating. If a juice costs 4.83 and a snack costs 2.17, round each to the nearest whole number to guess the total before you add. That is 5 plus 2, which is about 7.
Round decimals to the nearest one, tenth, or hundredth
Rounding a decimal is like asking: which landmark is this number closest to? The landmarks could be whole numbers like 3 and 4, or tenths like 3.4 and 3.5.
Step one is to find your landmark place. If you are rounding to the nearest one, watch the tenths digit. If you are rounding to the nearest tenth, watch the hundredths digit. You always peek one place to the right.
Step two is the decision. If the digit you are watching is 5 or more, round up. If it is 4 or less, round down, which really means the digit stays the same and everything after it becomes zero.
Try it with 3.47. Rounded to the nearest one, the tenths digit 4 is less than 5, so it rounds to 3. Rounded to the nearest tenth, the hundredths digit 7 is 5 or more, so 3.4 becomes 3.5. One number, two different answers, and both are correct because you rounded to different places.
The trickiest case is when the digit you keep is a 9 and you have to round up. Rounding 12.95 to the nearest tenth gives 13.0, not 12.10, because the extra tenth carries over into a whole new one.
Explore more
2 · Watch
به انگلیسیTake it off screen
Where it sits
Learn first
This opens up
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
15 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.