The first step is to get the dimensions of the tank in question.
Example: Let's suppose the above container
height:19", width 21", depth: 14"
First step is to convert inches to feet.
height 19" = 1.583 ft.,
width 21" = 1.75 ft.
depth 14" = 1.166 ft.
Next: multiply length, width, depth to get
the cubic footage of the tank.
[ 1.583 X 1.75 X 1.166 =
3.230 cubic feet ]
Now you're ready to calculate the capacity of
your tank. Simply multiply your answer by 7.48051945.
3.230 X 7.48051945 = 24.177178
Gallons per cubic foot
1 cubic foot = 7.48051945 US gallons
1 US gallon = 0.133680556 cubic feet
Now... that's all well and good except for a
First: Not all tanks are square. Specialty
dimension tanks and hull formed tank bottoms add problems with measurement.
This is where basic geometry, we
learned in high school, kicks in to help come up with tank
Go to the following web page for
a refresher concerning this situation.
You just have to measure carefully. Use the best measurement
of the square area of the tank and in most cases the non-measured area
won't be a factor. Keep reading for the reasons why.
Second: Since we are using the
exterior dimensions; plastic tanks have a thicker wall than
metal tanks and the inside dimensions of a plastic tank will be
somewhat smaller than the outside dimensions.
Third: Not all tanks will fill properly
without leaving an air bubble at the top of the tank. For example, a
long narrow tank with the fill and vent at one end, won't fill
completely if the fill/vent end is lower than the non vented end.
However, Not filling completely isn't always
a bad thing. Fuel will expand as it gets warmer. The air bubble in the
tank allows for fuel expansion without an overboard spill occurring.
Fourth: Usable fuel capacity is less than what
the fuel tank can hold. Running the fuel tank completely dry, while
under way, can cause a lean run condition of the engine, which is not
good for the engine.
In conclusion, always expect the actual
usable capacity to be less than your measurement, calculated above.
Have the tank as level as possible, when filling. Regularly inspect
the tank and hoses for condition and safety. If you are having a
problem filling the tank properly, consult professional help to
resolve the problem.