Just not today. :)

A couple of thoughts (though, I note that this is not from GC experience, damn it.) :)

The typical LP cylinder is a 20lb. tank.

Typically, a steel LP tank weighs about 17 lbs. I have a spun fiberglass tank that weigh 9lbs.  Each tank should have its engraved weight etched on the tank -- TW (tare weight) and then the numbers indicating the empty tank weight -- the only accurate way to measure the propane left in a propane tank is to weigh the filled or partially filled tank and subtract the empty weight.  Each gallon of liquid propane weighs 4.23 lbs. Divide  net weight by 4.23 to get the number of gallons currently in the tank.

Each gallon of propane contains 91,690 BTUs. Multiply the number of gallons by the number of BTUs contained in each gallon. To obtain the available BTUs.

Divide the available BTUs in the tank by the burn rate of your stove to obtain the total running time left for propane in the tank.

A couple of notes of caution.

20lb LP tanks have a safety reed switch that limits the flow for safety reasons to about 125,000 BTUs per hour. You can easily exceed that amount with T-connectors and a couple of stoves.

Current transportation regs. require these safety switches on all tanks 40 lbs or less. You can get a "roofers" tank that will hold 42 lbs of propane. Be careful about putting all your gas in one basket. A leak and failure to shut off your tank will quickly drain it. Multiple tanks help prevent a disaster.  All my trip members are encouraged to check the shut off valve every time they pass the tank if nothing is cooking.

Good luck.

FWIW