A 20 pound propane tank is the standard exchange cylinder holding about 4.7 gallons of propane, powering grills, patio heaters, and fire pits.
The “BBQ tank” is a portable steel LPG container and the most common size in exchange programs, according to the National Institute of Standards and Technology. Here’s what the collar numbers mean, what it can run, and the mistakes that get tanks turned away at the fill station.
How Big Is a 20 lb Propane Tank, Really?
A 20 pound tank measures roughly 12.3 inches across, 17.8 inches tall, holds about 4.7–5 gallons, and weighs close to 40 pounds full.
The “20 pound” label refers to propane capacity, not total weight. Propane expands with heat, so a tank filled to the brim on a cool morning can vent liquid on a hot afternoon.
That’s why tare weight matters. Every cylinder carries a permanent “TW” stamp covering the cylinder, valve, and permanent attachments. Subtract tare weight from total scale weight to get actual propane content — how fill stations verify they aren’t overfilling.
What Can a 20 Pound Propane Tank Run?
One tank runs a single outdoor appliance well and struggles to run several at once. Common uses:
- Gas grills — the classic pairing, good for many cook sessions per fill.
- Patio heaters and outdoor heat lamps — a full tank lasts several evenings.
- Fire pits and camping stoves — portable and easy to swap.
- RVs, food trucks, and generators — portable fuel for single appliances.
It will not replace a home heating setup or run a furnace, water heater, and grill at once. Those require a 100 lb or bulk home tank refilled by delivery.
Valve Types, OPD, and Compatibility
Most 20 pound tanks ship with an OPD (Overfill Prevention Device) valve and a Type 1/QCC1/ACME fitting matching standard grill connectors; some list POL safety plugs. Many fill stations won’t fill without an OPD, which Home Depot describes as required by law in most states.
Check your appliance connector before buying or refilling. A Type 1 hose connects directly to a QCC1/ACME cylinder; older POL equipment may need an adapter. Valve hardware is the most common mismatch.
Popular models include the Manchester Tank 10504 Vertical ACME/OPD Cylinder and the Flame King YSN230, which adds a built-in gauge.
The Numbers at a Glance
| Spec | Typical Value | Why It Matters |
|---|---|---|
| Propane capacity | 20 lb designed; often 15 lb net | Your real burn time per fill |
| Liquid volume | About 4.7–5.0 gallons | Rough runtime for a grill or heater |
| Full weight | Close to 40 lb | Plan for the carry |
| Dimensions | ~12.3 in x 12.3 in x 17.8 in | Fits standard tank holders |
| Valve type | Type 1/QCC1/ACME with OPD | Matches most grill connectors |
| Construction | Powder-coated steel | Rust resistance outdoors |
| Compliance | DOT (some also Transport Canada) | Legal to transport and refill |
If you’re comparing models, this roundup of tested 20 gallon LP tank options walks through what holds up outdoors.
Refill or Exchange?
Exchange programs trade convenience for cost — a flat fee for a prefilled tank. Refilling your own cylinder at a station like Tractor Supply typically delivers more propane per dollar, but the tank must pass inspection and the station must be open.
Both routes share one safety note: keep the tank at least 10 feet from heat sources, and never store it near an open flame or wood fire. NIST also emphasizes that safe contents are verified by weight, not by eye — the collar stamp and a scale are the only reliable way to know what’s inside, and the OPD exists to stop overfilling before the tank can vent liquid propane in heat.
FAQs
How long does a full 20 lb tank last on a grill?
On a mid-size gas grill, roughly 18 to 20 hours on low-to-medium, or fewer sessions on high heat. Patio heaters burn continuously, often getting about 10 hours from the same tank.
Can I put a 20 lb propane tank in my car?
Yes, if secured upright and the car is well ventilated. Keep it out of direct sun, don’t leave it in a sealed trunk on a hot day, and transport only DOT-compliant cylinders.
Is a 20 lb tank the same as a 5 gallon tank?
Close, but not exact. A 20 lb cylinder holds about 4.7 gallons; “5 gallon” is rounded shorthand. The 20 lb figure refers to weight, the gallon figure to liquid volume — the same standard cylinder.
References & Sources
- National Institute of Standards and Technology. “Liquified Petroleum Gas 20 Pound Cylinders” Source for capacity, tare weight, and exchange-program context.
- Tractor Supply. “Manchester Tank 10504 Vertical LP Cylinder with QCC1 OPD Valve” Source for valve type, dimensions, and DOT-4BA-240 spec.
- Home Depot. “Flame King 20 lb Propane Cylinder with OPD and Built-in Gauge” Source for OPD requirements and 10-foot heat clearance guidance.
