120 gallon propane tank chart
The 120 is the smallest size on this site. The 120 is its water capacity, and the gauge shows percent of that. Each 1% is 1.2 gal, so 50% is 60 gal. Tanks are filled to 80%, which is 96 gal. Ferrellgas and Propane101 both list 96 gal for this size.
Ferrellgas describes the 120 as a tank for homes with one or two propane appliances. So the useful question is how many days 96 gal lasts for those appliances, and the table further down answers it.
Your reading
Usable is the gallons between 80% and 20% (24 gal). I treat 20% as "empty" so there is time to get a delivery.
Gauge percent to gallons
| Gauge | In tank | Fill brings |
|---|---|---|
| 80% | 96 gal | 0 gal |
| 70% | 84 gal | 12 gal |
| 60% | 72 gal | 24 gal |
| 50% | 60 gal | 36 gal |
| 40% | 48 gal | 48 gal |
| 30% | 36 gal | 60 gal |
| 20% | 24 gal | 72 gal |
How long a 120 lasts
The daily figures come from Ferrellgas on propane use. A tankless water heater (about 40,000 Btu/h) uses around 1.5 gal a day. A gas range (65,000 Btu/h) uses 5 to 10 gal a month, and I took the top, 10 gal, or 0.33 gal a day. A fireplace (26,000 Btu/h) burns about 1 gal every 3 hours, and I assumed 3 hours a day. That last one is a guess, so adjust it to your habits.
| Appliances | Gal a day | Gal a month | From 80% | From 50% |
|---|---|---|---|---|
| Water heater only | 1.50 | 46 | 48 days | 24 days |
| Water heater and range | 1.83 | 56 | 39 days | 19 days |
| Water heater and fireplace | 2.50 | 76 | 28 days | 14 days |
| Water heater, range and fireplace | 2.83 | 86 | 25 days | 12 days |
Days count down to 20% on the gauge. They are arithmetic on the rates above, so your own readings are better. The box at the top and the calculator turn two readings into your rate.
What the tank looks like
The two sources list different sizes. Ferrellgas gives 54.5 in high and 30 in across. Propane101 gives 68 in long and 24 in across. Both call it a 120 gal (water capacity) tank, so the gauge works the same, but check the plate on yours. A 250 holds 200 gal at 80%, more than twice as much.
Propane101 notes that a tank this size generally serves one or a few appliances and is common in warmer climates with shorter heating seasons. A furnace alone burns about a gallon an hour while it runs (Ferrellgas), so I would not expect a 120 to carry a propane-heated house through a cold month. See how much propane a furnace uses.
Related pages
The 250 gallon propane tank chart and 500 gallon propane tank chart cover the larger tanks. All sizes are side by side on the propane tank percentage chart. For a delivery price, see cost to fill a tank.