*"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

*to confirm my measurement.*

**circumference of a circle**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**Now the formula for the circumference is

*. With that and a little bit of algebra it's easy enough to work out the radius...*

**2 × pi × r** Math

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

**and I was after the**

*radius***, so just multiply by two (or I could have just not multiplied pi by 2 above).**

*diameter* Math

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

*. 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).*

**77.35mm**Incidentally this is what my callipers said...76mm, which was spot on after all.

-i