Propane refill vs. exchange: what you actually pay
The short version: refill your own tank whenever a refill station is within a few miles. Exchange only when your tank is out of date or you're in a hurry.
How much propane is really in a tank
A standard 20 lb barbecue cylinder holds 4.7 gallons when filled to the 80% safety limit. Most swap-cage exchange tanks are filled to 15 lb — about 3.5 gallons — so a "full" exchange tank is about 25% short before you even fire up the grill.
The math
| Refill | Exchange | |
|---|---|---|
| Propane you get | up to 20 lb (4.7 gal) | usually 15 lb (3.5 gal) |
| Typical price | $3–$5 per gallon, so $14–$24 for a full 20 lb tank | $20–$27 per swap |
| Cost per pound of propane | roughly $0.70–$1.20 | roughly $1.35–$1.80 |
| Your tank | you keep it | you give it up — even a new one |
When exchange makes sense
Cylinders carry a manufacture date stamped on the collar. A new tank is good for 12 years; after that it needs a recertification (5 more years) or it can't legally be refilled. If yours is expired, a swap is the easiest way to get a valid tank. Exchange also wins at 9 pm when the refill counter is closed.
Tips at the refill counter
Most stations bill by the gallon, so a half-empty tank costs half as much — you're never paying for gas you already have, which is the other hidden cost of exchanging. Ask for the tank to be filled by weight or to the OPD stop; a good attendant does this automatically. Keep the tank upright and secured in the vehicle, and don't leave it in a hot car.