Same Math › Grades 3–4 › Rounding on a number line
How do kids learn rounding on a number line?
Kids place the number on a number line between two tens (or hundreds) and see which one it's closer to. 47 sits between 40 and 50, past the halfway mark, so it rounds to 50.
- Find the tens on either side: 40 and 50.
- Mark the halfway point: 45.
- 47 is past halfway, so 47 rounds to 50
Why schools teach it
Kids understand rounding instead of following a rhyme
Third graders round to the nearest 10 or 100 using place value understanding (3.NBT.A.1), and 4th graders round to any place (4.NBT.A.3). The number line shows what "nearest" means, so kids don't depend on a rule they half-remember.
It also explains the tricky case. A number exactly halfway, like 45, rounds up by convention, and the line shows why that's a choice, not a fact.
At the kitchen table
What to say, and what to skip
Say this
What tens is 47 between?
Where's the halfway point?
Is 47 closer to 40 or to 50?
What about 45? It's right in the middle.
By convention, halfway rounds up.
Skip this
- Teaching only the rhyme ("5 or more, raise the score").Fine as a reminder, but the number line shows why it works.
- Rounding to the wrong place.Rounding 347 to the nearest hundred looks at 300 and 400, not 340 and 350.
- Changing every digit.347 rounded to the nearest ten is 350, not 400.
See it in action
Rounding 362 to the nearest hundred
Find the hundreds on either side
300 and 400Mark the halfway point
350362 is past 350
362 rounds to 400
Rounding to the nearest ten instead gives 360. The place you round to changes the answer.
Free practice sheet
Make a rounding sheet
Loading practice sheet…
Fridge cheat sheets
Math Fridge Cheat Sheets
Every K–8 math method in one printable book (159 pages): a cheat sheet page like this guide, plus a practice sheet and its answer key for each, in Classic and handwritten Notebook styles. $9 one time, or all 7 subjects for $29.99. See all prices.
Teacher? This method has a classroom pack on TeachersPayTeachers: an anchor chart, a parent letter and practice sheets with answer keys, $4. See the pack
Parents: tell your child's teacher about this guide
Parents also ask
Why does 45 round up?
It's exactly halfway, so either answer is equally close. The convention is to round up.
Why do kids draw number lines for rounding?
The line shows what "nearest" means, which makes the rule make sense.
When is rounding used?
Mostly for estimating, which helps kids check whether answers are reasonable.
How is rounding different from estimating?
Rounding is one way to estimate. Compatible numbers are another.