inches to gallons

How do you convert gallons used out of a 55 gallon steel barrel into inches. I'm an ndustrial painter and use 55 gallon barrels of paint. There are 50 gallons in each barrel. I don't know the starting height, otherwise i could figure this out.

[JohnS]

Originally Posted by Unregistered

How do you convert gallons used out of a 55 gallon steel barrel into inches. I'm an ndustrial painter and use 55 gallon barrels of paint. There are 50 gallons in each barrel. I don't know the starting height, otherwise i could figure this out.

Well, it would be easier to measure the starting height on a new barrel, but the starting height can be calculated. The inside of the barrel is basically a cylinder, and
V = (pi/4)*d*d*h where pi = 3.14159, d is the inside diameter, and h is the paint height. However, if dimensions are inches, this is in cubic inches not gallons. There are 231 cubic inches per gallon. So solving for starting height

Hs = (231*50) / ((pi/4)*d*d) = 14709 / (d*d)
so you just need to measure inside diameter in inches.

Then remaining volume and remaining height of liquid are related as
V/50 = h/Hs
(use a dipstick to measure remaining paint, or stir rod)

[Mrs X]

Another way of looking at it is that if you have 50 gallons in a 55 gallon drum, it will be a proportion of the height of the drum, if the drum has straight sides. (each gallon will fill it up 1/55 of the height of the drum).

example: if your drum is 40 inches high, then 50 gallons will fill it up to
40 x 50/55 = 36 inches

30 gallons will fill it up to
40 x 30/55 = 22 inches

And so on.

Sometimes, you can tell how full they are by tapping on the side, or using an electronic stud finder to work out the level. Then the calculation just goes the other way:

If you have 15 inches left, then you have
15/40 x 55 = 20.6 gallons.

I have no idea how high a 55 gallon drum is though, so you would need to measure them, and use the real number where i put "40" above. you are more than welcome to post back here if what JohnS or I have said doesn't help.

[JohnS]

Some further Googling turned up a US government spec on 55 gal steel drums. Apparently the ID is 22.5". I really don't know if this applies to all, or only drums the government buys, especially now that there are plastic drums and exterior dimensions available on the web show considerable variation.

Assuming it is universally true (or roughly true), then the math above gives 32" liquid depth as the height for 55 gallon capacity, and for any other amount of liquid,
V/55 (gal) = h/32".

This assumes the interior is flat bottomed. Some drums have a conical sump insert at the bottom to minimize wasted contents. Without dimensional detail, I can't account for that.

Try this. Check out side of plastic drums to see if graduated marking are stamped on them. I measured between the stamped markings and came up with .5417 inches for each gallon. This works for me.

on a 22.5" diameter 55 gallon drum 34.5" long with two ribs. 1" is equal to 1.7 gallons.

This all applies only to drums that are standing up ( some good answers, though ! ). What if the drum is laying on it's side in a rack ? Would not the inches to gallon ratio then depend on the liquid level due to the round shape ?

[JohnS]

Originally Posted by Unregistered

This all applies only to drums that are standing up ( some good answers, though ! ). What if the drum is laying on it's side in a rack ? Would not the inches to gallon ratio then depend on the liquid level due to the round shape ?

That is correct. If it is level, we have some threads on "horizontal cylindrical tank" (use search). If it is not level, it is a major PITA.

How about Pi times R squared (of the inside diameter) times the hieght of the liquid divided by 231? 231 is the cubic inches in 1 gallon.

[rtrumpet]

Great thread. I also had no idea how this can be calculated so thanks for sharing the different methods.