How do I know how much propane is left in my tank?

The only ACCURATE way of telling how much propane is left in the container is to weigh it. On the collar of the cylinder will be a marking of TW## which is the weight of the cylinder in pounds with no propane in it. It might show T## in which case the cylinder is labeled in metric and the number refers to kilograms...

Weigh the cylinder and subtract the TW or T weight as applicable from that number. This is how much propane you have left.

Inline gauges are useless because they read pressure. Well the pressure in a propane tank changes with the temperature around it. So you could have anywhere from 0 PSI on a really cold day to 200PSI on an extremely hot day! An inline gauge will read close to full until the tank is almost empty and then the needle will drop like a stone in the last few minutes of burn time left in the tank. Dont waste your money on these!

The hot water thing works...sort of...You need to run the appliance first on high flame to get the liquid temperature inside the container to drop below the ambient air temperature enough to cause moisture in the air, if you are in an geographic area with enough humidity, to cause the tank to "sweat" and show where the liquid level is. You use gas to check the tank level and it is far from accurate. Weigh the Cylinder and you will know exactly where you are...

"If you pour hot water down the side of the tank, you can feel a temperature difference when you place your hand on it. The tank will feel cold up to the level where the propane is. Above that, the tank will feel hot where it contains only air."

Or, you can weigh it. A full "20 pound" tank for a grill holds 18 pounds of propane plus the weight of the tank, which is stamped on the collar. So, subtract the "tare" weight from the total and you should have the weight of the propane.

They actually sell a gauge you attach to the tank with a dial indicating the propane level. The one I just found online sells for $15.99.

If you pour hot water on the tank, you should be able to see a frost line. That is the gas level.

I use a digital thermometer and point it at the tank. There is a big drop in temperature at the level of the liquid. (I know most people don't have those thermometers, but it works for me). You can buy a gauge that you put inline and it will tell you.

Shake it.....if you hear liquid, your good to go. You only get charged for what it takes to fill it anyways unless you have Blue Rinos. Its actually cheeper to buy your own tank.