What Is The Formula For Circumferance For An 8" Diameter?

If the diameter = d = 8".

Radius = half of diameter, or 4".

Circumference = 2 * pi * r.

pi = 3.14159265.

So circumference =

0.5 * d * pi * 2, or just

Circumf = d * pi.

Which comes out as 8 * 3.14159265 = 25.1327412.  Inches, of course, don't lose the units in there.

That's a pretty big pipe, actually.

The formula of circumference for any round shape is given as follows:
Circumference =2 xPi x r

Another formula with respect to Diameter of the round shape is,
Diameter of circular shape =2 x Radius
                                        D =2R
Now the circumference equation will convert into;
Circumference= PixD
where the value of Pi= 3.14159265
Keep in mind that the value of Pi is dimensionless

Now for 8 inch diameter pipe D=8"
Circumference =pi x 8
circumference= 3.14159265 x 8
that comes out =25.1327412 inches
Hope you can calculate the circumference of all type of circular shapes.

25.12

Pi x D= circumference of circle
where Pi is = 3.142857142
where D is the diameter of the circle (ie: 8" or 8mm)

C=pieD