Rounding Numbers
What is rounding and why do we do it?
Rounding makes
numbers easier to work with. Here are two examples:
 If a house is 4 meters and 3 centimeters tall we would say it’s
4 meters tall. Most times this is close enough to describe the height
of the house.
 If you had a bucket with 598 marbles in it you could say you have about
600 marbles.
Remember, rounded numbers:
 are easier to work with in your head
 are only approximate  they do not tell you the exact answer
 are used when you just have to be close to the exact answer
Good rounding numbers resources from the web
Rounding
to significant places from the BBC
How to round numbers
 Highlight the digit that may change.
 Underline the digit on the right.
 Round the highlighted digit
 If the underlined digit is 5 or more the highlighted digit
is increased by 1.
 If the underlined digit is 4 or less the highlighted digit
stays the same.
 All the digits to the right of the highlighted digit are changed
to zeros.
Follow the menu options or use the following links to
learn more and to see examples of how to round numbers:
Try these rounding
numbers worksheets to help practice. These printable
number lines will also help with rounding numbers.
There are also 3 rounding worksheet generators here that will provide an unlimited number of questions on rounding.
"Rounding Words"
When you hear the following words you should know that they might
mean you have to round numbers:
 estimate
 approximately
 roughly
 ballpark
 close enough
 around
Rules For Rounding Numbers

Numbers can be rounded to the nearest ten,
the nearest hundred, the nearest thousand, the nearest
million, and so on.

If the number you are rounding is followed
by 5, 6, 7, 8, or 9, round the number up. Example: 79 rounded
to the nearest ten is 80

If the number you are rounding is followed
by 0, 1, 2, 3, or 4, round the number down. Example: 74
rounded to the nearest ten is 70

All the numbers to the right of the place
you are rounding to become zeros.

Rounded numbers are easier to remember
and easier to use.
Rounding Decimals
Try the worksheets below to practice rounding decimals to
the nearest thousandth, hundredth, and whole number. There is more here on how to round decimals.
Estimating using rounding
Rounding helps when we are looking for an estimates amount. An estimate
gives us a rough idea and it might be a little more or a little less
than the exact amount. Here’s an example:
Let’s say we wanted to buy 6 pizzas and we knew they were $19
each. To get a rough idea of the total cost we can round 19 to the
nearest 10 to get 20. We can then calculate 6 x $20 to give us
an estimate of $120 for the total cost. Estimating is also a good way
to check if our answers to a problem are reasonable.
By carrying out an estimate we can check that the answers to problems
are sensible.