Calculating Tank Volume

[Dillinger4]

I am trying to calculate the volume in gallons a cylindrical tank can hold with the dimensions 5' diameter and 10' length. V = D x D x 0.7854 x L works and yields 1,468 Gallons US either by measuring the tank in inches and dividing by 231 or measuring the tank in feet and multiplying by 7.48 but when using the formula V = pir^2l it doesn't work out.

[jemidiah]

Well, the volume of a cylinder is pi*r^2*h where r is the radius and h is the height. Your "V = pir^2" is at leaving off the h.

[Dillinger4]

The h in the formula V = pir^2l is the l at the end since the cylinder is lying down.

[passel]

You don't show your work, but I would assume perhaps you're not squaring the radius first, before multiplying by pi, then length, then your units to gallons conversion value.

It seems to work fine for me, i.e. using feet.

r * r          * pi                 l (length, aka h)  cubic ft to gal
2.5*2.5 = 6.25 * pi = 19.63495408 * 10 =  196.34954 * 7.48 = 1468.69456

[jemidiah]

...V = pir^2l...

Huh, I apparently missed that "l" repeatedly, sorry about that. You didn't give the important details so I suppose I latched onto a perceived typo instead.

[Dillinger4]

Ugh. I see what I was doing wrong. I squared the diameter and didn't multiply the result by 7.48. Thanks for the help jemidiah.