Igor Kromin |   Consultant. Coder. Blogger. Tinkerer. Gamer.

NOTE: This article is 3 years or older so its information may no longer be relevant. Read on at your own discretion! Comments for this article have automatically been locked, refer to the FAQ for more details.
I remember back in school thinking "when will I ever need to use this in real life" during math classes. Today was that day! I had to get the diameter of a copper water cooling pipe that's in my air conditioning utility cupboard and is quite hard to reach.

I do have callipers just for this purpose but when I tried to use them, I couldn't tell if they got all the way around the pipe or not. So I thought that I may as well use the formula for the circumference of a circle to confirm my measurement.

I used a flexible tape measure used for sewing to measure around the pipe, which gave me the circumference. In my case it was 243mm.

IMG_0320.jpg IMG_0321.jpg

Now the formula for the circumference is 2 × pi × r. With that and a little bit of algebra it's easy enough to work out the radius...
First write the formula and the measurements, which are equal one another
243 = 2 × pi × r
Substitute the value for pi, 4 decimal places is close enough
243 = 2 × 3.1415 × r
Multiply pi by 2
243 = 6.283 × r
Change sides for r and adjust to divide
r = 243 ÷ 6.283
Final result for radius
r = 38.675

Now that of course gives the radius and I was after the diameter, so just multiply by two (or I could have just not multiplied pi by 2 above).

Diameter is 2x the radius
d = r × 2
Substitute the value for radius
d = 38.675 × 2
Final result for diameter
d = 77.35

So the diameter of my pipe according to the calculation is 77.35mm. This is not a standard copper pipe size, which means my circumference measurement was wrong (confirmed later it was off by 5mm). It's important to get this measurement right, however it's not a show stopper if you just need an approximate value and can just match to the closest standard size (you're not likely to have non-standard sized pipes).

Incidentally this is what my callipers said...76mm, which was spot on after all.

IMG_0318.jpg IMG_0319.jpg


Skip down to comments...
A quick disclaimer...

Although I put in a great effort into researching all the topics I cover, mistakes can happen. If you spot something out of place, please do let me know.

All content and opinions expressed on this Blog are my own and do not represent the opinions of my employer (Oracle). Use of any information contained in this blog post/article is subject to this disclaimer.
comments powered by Disqus
Other posts you may like...