How to use estimation

Making a sensible guess or a rough calculation is known as estimation.

An estimate is not an exact calculation.

You can use estimation when you do not need to know an exact number or you can use it to quickly spot mistakes in calculations.

To learn how to estimate you need rounding skills.

Complete this interactive activity to understand how to use estimation. Then put your knowledge to the test.

Depending on how large the number is, or how near your estimation needs to be, you can round to 10, 100 or 1,000

Look at the calculation:

2,547 + 4,294

Let's use rounding to estimate the answer.

First, let's try rounding each number to the nearest 10.

The number 2,547 rounded to the nearest 10 is 2,550.

The number 4,294 rounded to the nearest 10 is 4,290.

2,550 + 4,290 = 6,840

Now let's try rounding to the nearest 100.

The number 2,547 rounded to the nearest 100 is 2,500.

The number 4,294 rounded to the nearest 100 is 4,300.

2,500 + 4,300 = 6,800

Finally, let's try rounding to the nearest 1,000.

The number 2,547 rounded to the nearest 1,000 is 3,000.

The number 4,294 rounded to the nearest 1,000 is 4,000.

3,000 + 4,000 = 7,000

But, which estimation was the closest?

The answer to the calculation is:

Rounding to the nearest 10 is the closest, but rounding to the nearest 100 was also close to the correct calculation.

Rounding to the nearest 1,000 is the quickest, but it's not as close to the correct calculation.

You can choose whether to round to the nearest 10, 100 or 1,000 depending on how accurate you need to be.