I can't tell by the picture it's volume, so I can't tell it's capacity. Nor do I know the BTUs (for example number BTUs/hour) used by your grill, stove, etc..?
Engraved on the side of the tank should be the letters "TW" (Tare Weight) then a number.
This number is the empty tank weigh in pounds.
The only way to
accurately measure the propane left in a propane tank is to
weigh it. (Bathroom scale)
The total density of propane is 0.493 per cubic meter, at 77 deg F, when converted it will be 4.11 lb.
Propane weighs about 4.1 lbs per US gallon at the above tempature.
Scale weight - TW = remaining pounds remaining.
Each pound of propane contains 21,600 BTUs. So, to find the remaining running time for the grill/stove divide number of BTUs remaining by number of BTUs per hour used by device= hours of run/burn time.
BTUs are provided by the device's manufacturer.
You can calculate capcity. Measure the container that your liquid propane is being stored in with a tape measure. You will need to find the radius of the top portion of the container, as well as the height.
Volume of a cylinder is: