How much propane does a 120-gallon tank hold?

How long your propane will last

The sums behind this tool are checked against 4 run times printed by a heater maker (ours must come out at or below them), and 31 checks in all, including the limits where it gives no number.

Why a 120-gallon tank doesn't hold 120 gallons

The size on the tank is its whole volume. Utah's State Fire Marshal says propane containers are filled to only 80% of their capacity, to allow for expansion.

So a full tank holds about 96 gallons. Propane suppliers' published size charts give the same usable figure, and it matches the sum: the tank's size times 80%.

Reading the gauge

The gauge on a big tank shows a share of the whole tank, not a share of a full fill. One propane supplier explains that a needle at 80% means the tank is completely full.

To turn a gauge reading into gallons, use the propane on hand calculator. If your gauge reads above 80%, ask your propane supplier or a certified propane technician.

How long does a 120-gallon propane tank last?

There's no single answer, because it depends on what the propane runs. The sum is simple: gallons in the tank, times the heat in a gallon, divided by your appliance's input in Btu per hour.

For run times we use 91,300 Btu per gallon, the lowest official figure we hold, so the answer errs on the short side. The calculator also works at each appliance's full rating and rounds down.

The calculator takes one appliance at a time: type in its rating from the rating plate and the hours a day it runs. Each answer is how long the tank would last if that appliance were the only one using it. For a whole house, ask your propane supplier about your past deliveries.

Size, weight and dimensions

Length, width and empty weight vary from one maker to another, so we don't give figures for them. Check the data plate on the tank, or ask your propane supplier.

Where the tank sits, and how far it must be from your house, depends on its size and local code. Ask your propane supplier or your local fire marshal, and have tanks and lines installed by a certified propane technician.

Next size up or down

The nearest sizes we cover are the 100-lb cylinder below it and the 250-gallon tank above it. The propane tank sizes chart lists them all side by side.

Questions people ask