# Thread: Surface area for cylinder does not work unless in CM?

1. ## Surface area for cylinder does not work unless in CM?

I really do not like to have an understanding hanging when learning, as it could crop up somewhere else in the future.

In my class, this question was simply to find the surface area of a cylinder that is 1 metre in diameter, and 2 metres in height.

The instructor had stated "You must convert it in to centimetres", and I did and it had worked - and I did not understand.

My two calculations that confuse me:

m:
$SA = 2\pi(.5)^2 + 2\pi(.5)(2) = 7.852 m^2 = 785cm^2$
cm:
$SA = 2\pi(50)^2 + 2\pi(50)(200) = 78539.82 cm^2$

It seems the two numbers are the same, even though wrong radix, however why can you not use metres? Does the calculation require it? That would not make sense, as (at least I believe) people would obviously use inches as a diameter in the states and other things.

It may just be something so simple, it is really bothering me.

Alexei.

2. ## Re: Surface area for cylinder does not work unless in CM?

you have to be careful
1 m = 100 cm
1 m^2 = 10000 cm^2
1 m^3 = 1000000 cm^3

3. ## Re: Surface area for cylinder does not work unless in CM?

Originally Posted by Amer
you have to be careful
1 m = 100 cm
1 m^2 = 10000 cm^2
1 m^3 = 1000000 cm^3
Thank you, that perfect. Now I can move on and know it with a little more confidence.

Alexei.