What is the equation to figure out how many gallons in a tank?

Thanks

square/rectangular tanks:

length*height*width = vol

round tanks:

diameter*diameter*0.785 = vol

if tank dimensions in inches
gallons = vol * 0.00433

if tank dimensions in feet
gallons = vol * 7.48

if tank dimensions in meters
gallons = vol * 248

gallons are US liquid measure

I have always done it like this -

Square tank is width times height times length divided by 231.

Round tank is Pi (3.1416) times diamter times length divided by 231.

All measurements in inches.

Example 4" square tube bumper -

4 X 4 X 29 = 464 cubic inches/231 = 2.009 gallons

Example 4" round bumper -

4 X 3.1416 X 29 = 364.43 cubic inches/231 = 1.578 gallons.

If yer no good at math...
drive around with small jerry can of gas till u run out. Put in 5 Gallon jerry & go to gas station. The pump will tell you how big yer tank is. :D :D :D