Yes, we get questions from all directions at Kele tech support. This one started out as a level measurement problem, but it quickly turned residential in nature. Here’s how the Kele Engineering team handles it:
Somewhere on your propane tank is stamped the empty, or tare, weight. It’s usually on the protective collar around the valve with the designation T. Mine says T17.1, which indicates Tare = 17.1 pounds.
Weigh the tank with a scale that’s accurate in the under-50-pounds range, or else weigh yourself on an accurate scale both with and without the tank in your arms and take the difference in the two readings. At Kele R&D, we tend to prefer the Futek LTH500 super-high-precision load cells for critical pre-ribeye measurements, but we’re willing to compromise at hot dog time.
The difference between measured weight and tare weight is available fuel in pounds. Remember, you only know the tare to three significant digits, so don’t strain your calculator on the math.
So now you know how many pounds of propane are left. How long will it last?
Find the rated burner input for your grill. It should be on the nameplate or in the original owner’s manual. Our grill says 42,000 BTU/hr.
According to the National Fuel Gas Association, propane is good for about 20,000 BTU/lb.
Therefore, my grill will burn (42,000 BTU/hr) / (20,000 BTU/lb) or 2.1 lb/hr at the maximum burner setting. Your mileage will vary, depending on cleanliness, ambient temperature, wind speed, and a number of other conditions. It won’t vary much, though, for identical burners.