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A typical 40,000 BTU three-burner gas grill uses about 0.44 gallons of propane per hour — roughly 1.8 pounds — with every burner on high. That costs about $1.86 an hour at a refill station, or closer to $3 an hour if you buy exchange cylinders. A realistic cookout of 15 minutes preheat plus 30 to 45 minutes cooking uses about a quarter of a gallon, or roughly $1 of gas. A full 20-pound cylinder therefore covers close to 20 average cookouts, and most households get through two or three tanks a season.
The formula, and where the numbers come from
Propane contains about 91,500 BTU per gallon, and weighs about 4.2 pounds per gallon. A "20-pound" cylinder is filled to 80 percent of its volume for safety expansion, which is about 4.6 gallons or roughly 420,000 BTU of usable energy.
Your grill's BTU rating is the total it consumes per hour with everything on high. So:
- Gallons per hour = grill BTU ÷ 91,500
- Pounds per hour = gallons per hour × 4.2
- Hours per full tank = 420,000 ÷ grill BTU
Worth noting explicitly, because it is the most common misreading: BTU is a measure of fuel consumed, not heat delivered to food. A high BTU number on a poorly insulated grill means it burns more gas to hold the same temperature, not that it cooks better. That distinction matters when shopping, and it is covered in grill BTUs explained.
Consumption and cost by grill size
| Grill rating | Gallons/hr | Pounds/hr | Hours per 20 lb tank | Cost/hr at refill | Cost/hr at exchange |
|---|---|---|---|---|---|
| 20,000 BTU (portable, 2-burner) | 0.22 | 0.9 | ~21 | ~$0.93 | ~$1.54 |
| 30,000 BTU (3-burner) | 0.33 | 1.4 | ~14 | ~$1.39 | ~$2.31 |
| 40,000 BTU (3-burner, larger) | 0.44 | 1.8 | ~10.5 | ~$1.86 | ~$3.08 |
| 50,000 BTU (4-burner) | 0.55 | 2.3 | ~8.4 | ~$2.32 | ~$3.85 |
| 60,000 BTU (5-burner or 4+side) | 0.66 | 2.8 | ~7 | ~$2.79 | ~$4.62 |
Refill costs are figured at about $4.25 a gallon and exchange at roughly $25 for a cylinder filled to 15 pounds, which works out near $7 a gallon. Both vary regionally and seasonally; check local pricing before treating these as exact. These figures also assume every burner on high, which almost nobody does for a whole cook.
What a real cookout actually uses
Flat-out consumption is the wrong figure for budgeting, because grilling is mostly preheat plus partial-burner cooking.
Take a 40,000 BTU three-burner grill and a normal session: 15 minutes with all three burners on high to preheat, then 40 minutes with one burner at medium and one off while the food cooks. That is about 10,000 BTU for the preheat and roughly another 10,000 BTU for the cook — about 20,000 BTU total, or 0.22 gallons, close to a dollar of gas.
| Usage pattern | Propane per session | Approx. cost | Sessions per 20 lb tank |
|---|---|---|---|
| Quick burgers, 30 min total | ~0.15 gal | ~$0.65 | ~30 |
| Typical cookout, 55 min | ~0.22 gal | ~$0.95 | ~20 |
| Long indirect cook, 2.5 hr | ~0.55 gal | ~$2.35 | ~8 |
| All-day party, 5 hr mixed | ~1.5 gal | ~$6.40 | ~3 |
Over a season of 30 cookouts, that is roughly 6.6 gallons — about one and a half tanks and under $30 in fuel. Propane is rarely the expensive part of owning a grill.
What pushes consumption up
Cooking with the lid open. The single biggest waster. An open lid lets most of the burner output convect straight past the food, so you compensate with higher settings for longer. Closing the lid can halve gas use on the same cook.
Cold weather. Propane vaporizes more slowly at low temperatures, so tank pressure falls, output drops and the cook takes longer. Below about 20F a nearly empty cylinder may struggle to feed a large grill at all. Wind compounds it by stripping heat off the cookbox.
A grill that leaks heat. Thin cookboxes, warped lids and worn gaskets all mean more gas for the same grate temperature. This is the practical reason a well-built grill with a moderate BTU rating often out-cooks a cheap one with a bigger number.
Actual leaks. A weeping regulator connection can empty a tank silently. Brush soapy water on the hose, regulator and valve connections with the tank open and look for bubbles. Never test with a flame.
Preheating longer than needed. Ten to fifteen minutes is enough for almost any grill. Twenty-five minutes of preheat before every cook adds up to a tank a season on its own.
Telling how much is left in the tank
Propane cylinders have no gauge, but there are two reliable methods. Weigh it: every cylinder is stamped with a tare weight, marked TW, which is the empty weight in pounds. Put the tank on a bathroom scale, subtract the tare weight, and what remains is the propane. A full tank reads tare plus about 20 pounds.
Or use hot water: pour a cup of hot water down the side of the tank and run your hand down it. The metal is cool where liquid propane is absorbing heat and warm above it, and that boundary is the fill level. It is surprisingly accurate. Our guide on checking a propane tank without a gauge covers both in more detail, and how long a propane tank lasts works the same numbers as burn time rather than cost.
Cutting propane use without cooking worse
- Keep the lid closed. The highest-return habit by a wide margin.
- Preheat 10 to 15 minutes, not 25. Set a timer if you tend to wander off.
- Use two zones. Running one burner high and one off uses less gas than three on medium, and cooks most food better.
- Turn burners down once the grill is at temperature. Holding 400F takes far less gas than reaching it.
- Keep the grill clean. Blocked burner ports and grease-caked heat tents both reduce efficiency. See how to clean a grill.
- Refill instead of exchanging where you have the option, and keep a spare tank so you are never mid-cook with an empty one.
- Shelter the grill from wind, without ever enclosing it.
Propane safety, non-negotiable
Leak testing. Brush soapy water onto the hose, regulator and tank valve connections with the cylinder valve open and the burners off. Bubbles mean a leak: close the valve, tighten or replace the fitting, and retest. Never check for a leak with a flame.
Disconnecting. Close the cylinder valve first, always, before you unscrew the regulator — and close it whenever the grill is not in use, not just when the tank comes off.
Storage. Never store a spare cylinder indoors, in a basement, in a crawlspace or in an attached garage. Cylinders belong outside, upright, in shade, away from heat sources and ignition sources. Never leave one in a hot car.
Never grill or store a lit grill in a garage, a carport, a covered balcony or any enclosed space. Propane and charcoal both produce carbon monoxide, which is colorless and odorless; the CPSC records roughly 20 deaths and about 400 emergency-room-treated injuries in the United States each year from carbon monoxide produced by charcoal alone, and is explicit that opening a window or running a fan does not make it safe (CPSC, Carbon Monoxide Information Center).
Placement. Keep the grill well clear of the house, siding, deck railings and overhanging branches while it is running, and never leave it unattended, as the NFPA grilling guidance advises.
Cylinder age. Propane cylinders must be requalified 12 years after their manufacture date, which is stamped on the collar, and periodically after that. A refill station will refuse an out-of-date tank; an exchange cage effectively resolves it by giving you a recertified cylinder.
Where to go next
If your grill seems to burn gas without getting hot, the cause is usually clogged burner ports or a tripped regulator rather than the tank — see why a gas grill will not get hot. For winter storage of tanks, leaving a propane tank outside in winter covers what is and is not safe.
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