What is 400 times pi?

400 is an integer and pi (π) is the ratio of a circle's circumference to its diameter and is best known as 3.14. However, pi is an irrational number with an infinite number of decimals: 3. 1 4 1 5 9 2 6 5 3 5 8 9 7 9 and so on.

For most practical purposes, 400 times pi is simply 400 times 3.14 as illustrated below:

400 x 3.14 =
1256

You can make the answer more accurate by using more decimals of pi. For example, here is 400 times pi with 12 decimal numbers:

400 x 3.141592653589 =
1256.6370614356

If 400 is the diameter of a circle, then 400 times pi is the circumference of that same circle. See definitions and explanations below to find out why!

Definitions

The radius (r) of a circle is the distance from the center of the circle to the edge of the circle. The diameter (d) of a circle is the distance from one point on a circle through the center to another point on the circle. In other words, 2 times the radius equals the diameter.

Like we said above, pi is the ratio of a circle's circumference to its diameter. Therefore, we can use pi to calculate the area and circumference of a circle.

Area

The formula to calculate the area of a circle is πr^2 (pi times radius squared). If 400 is the radius, then the area of the circle is pi times 400 squared:

3.14 x 400^2 =
1256.6370614356

If 400 is the diameter, then you first have to divide 400 by 2 to get the radius and then calculate pi times radius squared:

400 / 2 = 200
3.14 x 200^2 =
125600

Circumference

The formula to calculate the circumference is 2πr (2 times pi times radius). If 400 is the radius, then the circumference of the circle is 2 times pi times 400:

2 x 3.14 x 400 =
2512

If 400 is the diameter, then you first have to divide 400 by 2 to get the radius and then calculate 2 times pi times radius:

400 / 2 = 200
2 x 3.14 x 200 =
1256

Note: Instead of dividing 400 by 2 above, you could also have simplified the formula because 2 times pi times radius is the same as pi times diameter. Thus, like we said at the top of this page, 400 times pi is the circumference of the circle if 400 is the diameter.

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What is 401 times pi?
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