How to read your propane gauge

Lift the dome. The gauge is under the dome on top of the tank, next to the fill valve. The dial is a circle of numbers, usually 5 to 95, with a needle.
Read the percent. The needle points to the percentage of the tank’s total capacity that is liquid propane. If it points at 50, the tank is about half full.
Remember 80 is full. Propane tanks are never filled past 80% of capacity — the top fifth stays empty so the liquid has room to expand as it warms. A gauge that reads 80% after a delivery is a full tank, not a short fill.
Multiply by your tank size. The percent times the tank’s water capacity is the gallons in the tank: 50% of a 500-gallon tank is 250 gallons. That is the whole math — this tool just does it for you and turns it into days.

Gauge not moving?

Float gauges stick, especially on older tanks — sometimes for months, which is how people run dry on a gauge that reads half. Check it against your last delivery ticket: if the driver put in 200 gallons and the needle barely moved, the gauge is lying. Tell your supplier when you order — they can replace it, and a wireless tank monitor is the fix if you would rather not watch the dial at all. Do not open any valve under the dome yourself; the gauge is the only thing under there you should touch.

What moves the number

Burn rate is the whole game. A 100,000 BTU furnace burns about a gallon an hour when it is actually running, and in cold months it runs roughly 2–6 hours a day — that is 2–6 gallons a day for heat alone, before the water heater (about 1–1.5 gallons a day) and the stove (about a quarter gallon a day). Your thermostat, insulation, and house size move the days more than the tank math does.
Cold snaps shorten everything. EIA’s seasonal average for a propane-heated household is about 493 gallons over the November–March season — roughly 3.3 gallons a day averaged out — but a 10%-colder winter pushes that to 530 gallons. A week of deep cold can burn what a mild month does.
The 80% rule. A “full” 500-gallon tank holds 400 gallons, not 500. A gauge reading of 30% is 150 gallons in the tank, and at 5 gallons a day that is a month of heat — at 8, it is under three weeks.
Gauge precision. Most dials read in 5% steps, and 5% of a 500-gallon tank is 25 gallons — about five days of winter heat. A reading between two marks is a guess either way; round down when you are deciding whether to call.

Honest limits

Aboveground tanks only. These numbers assume the standard aboveground ASME tanks (120, 250, 500, 1,000 gallons water capacity). Underground tanks are filled to about 85%, not 80%, and use the same percent-times-capacity math with a different full point.
Other sizes exist. 60-gallon and 320/325-gallon tanks are out there. The gauge math still works for any tank — percent times its water capacity, printed on the tank’s nameplate — but this tool only lists the four common sizes.
Burn presets are rules of thumb. They come from dealer experience and the EIA seasonal average, not your furnace’s meter. Two gauge readings a week apart in cold weather, converted to gallons and divided by the days between, is the truest number you will get.
Days are total gallons, not a safe minimum. Every gallon in a propane tank is burnable — there is no sludge dead zone the way heating oil has. The reason not to run it to zero is the leak test and relight, not the fuel.

Frequently asked questions

Why does my gauge never read 100%?

It is not supposed to. Propane is stored as a liquid that expands as it warms, so tanks are filled to a maximum of 80% of their water capacity, leaving the top fifth as vapor space. The dial runs roughly 5 to 95, and 80% after a delivery means full.

How many gallons does a “full” 500-gallon tank actually take?

About 400 gallons. Drivers fill to 80% of the tank’s 500-gallon water capacity. That is also why a delivery after a 30% reading is about 250 gallons (80% minus 30%, times 500), not 350.

What happens if my tank runs dry?

Call for a delivery and tell the supplier the tank is empty. Every pilot light in the house will be out, and a qualified technician must leak-test the system before the gas is turned back on — in many states that test is legally required before refilling an empty tank, and it is usually a paid service call on top of the delivery. Never turn the gas back on yourself.

My gauge hasn’t moved in weeks. Is it broken?

Probably stuck. Float gauges gum up and freeze in place, sometimes reading half a tank for months. Compare the needle against your last delivery ticket — if the gallons delivered do not show up on the dial, the gauge is dead. Tell your supplier when you order and ask about a replacement or a wireless monitor.

My tank isn’t 120, 250, 500, or 1,000 gallons. What now?

The gauge math still works — a reading of 50% means roughly half the tank’s water capacity, which is printed on the tank’s nameplate. The order thresholds still apply too: call at 30% if propane is your main heat, and never let it drop below 20%.

How do I figure out my real daily burn?

Write down the gauge percent today and again in seven days of cold weather. Convert both to gallons (percent times tank size), subtract, and divide by seven. That number — your house, your weather, your thermostat — beats any preset on this page.

Sources

EIA — Winter Fuels Outlook, Table WF01 — the average propane-heated household uses 493 gallons over the November–March season (2025–26 forecast), 530 gallons in a 10%-colder winter; the season-average anchor behind the burn presets
Propane Education & Research Council — Safety Guide for Propane Users — a qualified professional must check the system for leaks when the gas is turned back on after a run-out; never turn the gas on at the tank yourself; pilots must be relit properly
Ferrellgas — Here’s Why Your Propane Tank Is Never Full — the 80% fill rule, the gauge reading as a percent of water capacity, and the standard 250/500/1,000-gallon residential sizes
Cape Cod Oil & Propane — Why Isn’t My Propane Tank Completely Full? — the 80% rule and expansion space, the 120-gallon → 96 and 500-gallon → 400 fills, and never letting the level drop below 20%
Great Valley Propane — How to Read a Propane Tank Gauge — the gauge-percent-to-gallons chart for 120/250/500/1,000-gallon tanks, the 20% floor, and calling at about 30% when propane is the primary heat source
HVACSeer — How Many Gallons of Propane Does a Furnace Use? — a 100,000 BTU furnace burns about 1.09 gallons per hour at full fire (91,547 BTU/gallon), running 2–6 hours a day in colder months for 2–6 gallons a day
EngineerFix — How Long Does 250 Gallons of Propane Last? — a home heating primarily with propane uses roughly 3–10 gallons a day, up to 8–15 in the most intense use; corroborates the winter and deep-cold presets
Haffner’s — How Much Propane Does a House Use Per Day? — furnace 1–2 gallons per hour when running, water heater 1–1.5 gallons a day, stove about 0.25 gallons a day
Ohio Propane Gas Association — Propane Basics and Safe Use — a leak check is required in many states before the gas is turned on after a run-out; pilots go out when the tank empties
Propane Depot — Why Was My Propane Tank Not Filled to 100 Percent? — underground tanks fill to about 85% because the ground insulates them; single dealer source, used only for the underground-tank caveat

Deciding when to call is half the job — the other half is price. Run your last delivered price through our propane price checker, and read how home heating works for rural homes for the full fuel picture. If you are weighing a contract instead of will-call, our propane and oil contract decoder explains pre-buy, price-cap, and budget plans in plain English.