I realized that I was probably replacing the propane tank on our grill with a full tank before we really needed to
because I was not sure how much longer it would last so I found out how to calculate the remaining time.
This is a very simple way to determine how much remaining time you have in the grill propane tank.
You need to know 3 numbers to do it:
grill BTUs (how much gas it burns per hour), 12000 is a typical value
empty tank weight, this should be written next to TW (tare weight) on the collar/top of the propane tank,
16.6 is typical
current tank weight, get a bathroom scale and put the tank on it
Empty tank weight (lbs, 16.6 typical)
Grill BTUs (12000 is typical)
Current tank weight (lbs)
Remaining gas (lbs)
Remaining time (hours)