Propane tank gauge

 

1.  Take the tank off and weigh it on a bathroom scale.  There is a tare weight marked on the tank which is what the tank itself weighs.  Subtract that from the total and you'll know exactly how many pounds of propane you have.  But, this method is a pain.

 

2. Use a stick-on gauge or screw-on gauge.  The stick-on gauges are basically thermometers which show you where the temperature changes on the outside of the tank.  I think they can fail in cold weather and do the same thing as #4 below so I don't recommend them.  The screw-on gauges meaure the pressure of the gas.  The problem with them is the pressure of the gas is basically the same all the time until the very end - and its unlikely you'll be staring at the gauge at that point, even if you were its too late already.  LP is stored as a liquid which sits at the bottom of the tank, and evaporates into the empty space above it.  That gas is what you use.  The surface area of the liquid stays the same all the way down until it hits the bottom shoulder (where the tank curves) and it is at that point that the pressure begins to drop.  Again, too late to do you much good.

 

3.  In-tank gauge or translucent tank.  You can buy tanks that have a float in them like your car's gas tank, so their gauge will be accurate.  You can also buy a tank that isn't made of steel.  I think it is fiberglass & resin.  So you can see the level with them.  The problem with both of these tanks is they are much more expensive.

 

4. The "hot water method".  Take a cup of hot water, pour it slowly down the side of the tank from the top shoulder.  Keep the water in one line, don't pour it all over the tank.  Wait a few seconds, then run your finger down the side of the tank where the water was.  The top of the tank will still be hot.  It will abruptly turn cold where the liquid begins because it can absorb the heat.  The line where it changes is where your fuel level is.  Note that if you do this to a fully-filled tank the line won't be at the very top.  LPG tanks leave the top 20% empty for the gas and to allow for thermal expansion.  This is the easiest and cheapest method and is the one I use.