# Circumference

#### speedy

##### New member
If Earth is a perfect sphere of 4,000 miles radius what is it's circumference in miles?

#### Dr.Peterson

##### Elite Member
Since Earth is not a perfect sphere of 4000 miles radius, I could logically say anything I want and my statement would be "true"; but that wouldn't be what you're asking. You mean, "If Earth were a perfect sphere of 4,000 miles radius what would be its circumference in miles?"

Do you know the formula for the circumference of a circle? It's $$\displaystyle C = 2\pi r$$.

Replace $$\displaystyle r$$ with 4000, and do the calculation.

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#### Subhotosh Khan

##### Super Moderator
Staff member
If Earth is a perfect sphere of 4,000 miles radius what is it's circumference in miles?
Circumference of a sphere is defined as the circumference of the great circle around the sphere

Circumference C = 2 * $$\displaystyle \pi$$ * radius

Continue....

#### speedy

##### New member
Since Earth is not a perfect sphere of 4000 miles radius, I could logically say anything I want and my statement would be "true"; but that wouldn't be what you're asking. You mean, "If Earth were a perfect sphere of 4,000 miles radius what would be its circumference in miles?"

Do you know the formula for the circumference of a circle? It's $$\displaystyle C = 2\pi r$$.

Replace $$\displaystyle r$$ with 4000, and do the calculation.
Have i worked it out correct = 25132.74 miles

• Dr.Peterson

#### Jomo

##### Elite Member
Have i worked it out correct = 25132.74 miles
I don't know as you never said what the circumference equals. Please give complete answers.

#### Levido

##### New member
Have i worked it out correct = 25132.74 miles
Yes, 25132.74 is the correct answer to 2 decimal places for the calculation 2*pi*4000 (in miles)

#### toponlinetool

##### New member
Formula for sphere can be calculated as 2*pi*r
Here r= 4000 miles,
Circumference= 25132.74 miles