When i was working in metal fabrication, I was struggling to get the exact perimeter of my project even using every formula or any way that I was known. But later on one of my colleague told me this formula that up to now; that I'm not anymore on that arena; was never disappeared on my mind.
I decided to share it to everybody as a reference and not to reform the traditional formula that was taught by the books and universities.
Formula: C(in cm) = d(in inch) x 8
whereas: C - is circumference in centimeter
d - is diameter in inches (every diameter must be in inches)
8 - is constant
Example: d = 10.25"
Solution: C = 10.25" x 8
Answer: C = 82cm
Try this!