How To Figure A Diameter From A Circumference?

The formula for finding out the circumference of a circle is:
Circumference = 2(pi x r)
Where r is the radius.
Now, the value of pi is always taken as 3.14. If we have the value of the circumference, we can find the value of the radius.
Let's suppose that the circumference is x. Therefore, to find the radius:

C = 2(Pi.r)
x = 2(3.14.r)
x = 6.28 (2r)
x = 12.56r
r = x/12.56

Now the diameter is always twice the length of the radius. Therefore, any answer that you get for the radius, you just have to multiply it by 2 to obtain the value for the diameter.
In this case:
Diameter = 2xr
Diameter = 2(x/12.56)

Let's do this with an actual number. Supposing the circumference is 20cm, the radius would be:
20 = 2 (Pi.r)
20 = 2 (3.14r)
20 = 6.28r
r = 20/6.28
r = 3.19 cm

Diameter = 2r
Diameter = 3.19 x 2
  = 6.38 cm

Diameter x  Pi = circumference

diameter = circumference / pi

Pi = 3.141592654

7 1/2 / 3.141592654 =

I have a circumference measurement of 28 1/2 inches and I need to know the diameter of same

The circumference of a mirror is 185 cm
find the diameter of the mirror

Diameter = Circumference/Pi

pi = 3.14 or 22/7

Circumference 1:  c1= 7 1/2 = 15/2

Circumference 2: C2= 14 1/2 = 29/2

D1=c1/pi

= (15/2) / (22/7)
= 15/2 x 7/22
=105/44
= 2.386 inches
 
D2 = c2/pi
= (29/2) / (22/7)
= 29/2 x 7/22
= 203/ 44
= 4.614 inches.

The circumference of a circle is;

Circumference= 2*pi*r

Pi= constant= 3.14

r= radius

If we are given circumference of the circle, then the radius of the circle can be calculated by the formula;

radius = circumference/ 2*pi

The radius of a circle is equal to the half of diameter of the circle.

Radius = Diameter/ 2

Diameter= 2 radius

So, the diameter of the circle can be calculated by taking twice of the radius.