How much propane is in an exchange tank?

Blue Rhino and AmeriGas both say their exchange tanks hold 15 lb of propane, about 3.6 gallons.

How much propane does a 20 lb tank hold when refilled?

Up to about 20 lb, or roughly 4.7 gallons, since propane weighs about 4.2 lb per gallon.

Is refilling or exchanging cheaper?

Divide the exchange price by 3.6 to get the price per gallon you are really paying, then compare it with the refill price per gallon. A refill also lets you keep any propane left in your tank.

Refill vs. swap: which propane option costs less?

Swapping a tank at a store cage is quick. Refilling your own tank usually gets you more propane. The trick is comparing them by the gallon, not by the sticker price.

The short version

Exchange tanks hold 15 lb of propane. Blue Rhino says its tanks are "precision-filled to 15 lbs," and AmeriGas says its tanks hold "a net weight of 15lbs." Sources: Blue Rhino FAQ, AmeriGas
A "20 lb" tank can hold up to 20 lb. The federal weights-and-measures office (NIST) notes that most exchange cylinders are filled and labeled to 15 lb, even though the tank can safely hold 20. Source: NIST
Propane weighs about 4.2 lb per gallon, so a full 20 lb tank is about 4.7 gallons, and a 15 lb exchange tank is about 3.6 gallons. Source: U-Haul 20 lb tank specs
With a swap, leftover propane goes back with the old tank. With a refill, you only pay for what goes in. U-Haul, for example, says it has no minimum fill charge. Source: U-Haul

How to compare prices

Exchange: divide the swap price by 3.6. That's what you're really paying per gallon.
Refill: look at the posted or quoted price per gallon. A full 20 lb fill is about 4.7 gallons, minus whatever is still in your tank.
Compare the two per-gallon numbers. If the swap works out higher per gallon, refilling is the better deal, and you also get about 1.1 more gallons per tank.

We don't make up prices. Few propane sellers post a price online. In Utah we found three on the businesses' own websites (none of the pages are dated, so they may be out of date):

Dixie Forest RV Resort (Panguitch) (Panguitch): $3.89/gal, seen Oct 28, 2026 on rjourney.com.
Flying J #744 (Ogden) (Ogden): $4.00 (posted "Propane" price; unit not shown), seen Oct 28, 2026 on pilotcompany.com.
Love's Travel Stop #518 (Springville) (Springville): $3.99 (posted "PROPANE" price; unit not shown), seen Oct 28, 2026 on loves.com.
Love's Travel Stop #686 (Brigham City) (Brigham City): $3.99 (posted "PROPANE" price; unit not shown), seen Oct 28, 2026 on loves.com.
Love's Travel Stop #792 (Green River) (Green River): $3.99 (posted "PROPANE" price; unit not shown), seen Oct 28, 2026 on loves.com.
Love's Travel Stop #835 (Fillmore) (Fillmore): $3.99 (posted "PROPANE" price; unit not shown), seen Oct 28, 2026 on loves.com.
Pit Stop Propane (Curt's Car Wash) (Draper): $3.79/gal, seen Oct 28, 2026 on curtscarwash.com.
Wagons West RV Park (Fillmore) (Fillmore): about $3.49/gal ("lowest price"), seen Oct 28, 2026 on wagonswestrv.weebly.com.
Love's Travel Stop #335 (Cedar City) (Cedar City): $3.99 (posted "PROPANE" price; unit not shown), seen Oct 28, 2026 on loves.com.
Love's Travel Stop #581 (Salina) (Salina): $3.99 (posted "PROPANE" price; unit not shown), seen Oct 28, 2026 on loves.com.

At $3.79 a gallon, a full 4.7-gallon fill of an empty 20 lb tank would be about $17.80. To beat that, a swap would need to cost less than about $13.65 (3.6 gallons × $3.79). Around St. George, nobody posts a price, so the only local figures come from customer reviews:

B&L Propane (Hurricane): one customer said they "paid 2$ per gal" filling an RV (Nov 2025). Reported in a customer review: source At that rate, a full 4.7-gallon fill would be about $9.40, but the price may have changed.
Warren Energy Hurricane: one customer mentioned about $11 for 3 gallons (Jan 2025). Reported in a customer review: source

Paid for propane recently? Report the price →

Quick calculator

Type in prices you've seen. Nothing is filled in for you.

Exchange (swap) price, $ Refill price per gallon, $ Propane left in your tank, gallons

Enter an exchange price and a refill price to compare.

When swapping still makes sense

Your tank is past its date or damaged. Exchange companies take old tanks in trade, while a refill station may need to recertify it first. One B&L Propane customer said a recertification cost about $5. Reported in a customer review: source
It's late at night or a Sunday. Most local refill stations keep business hours, while some exchange kiosks are self-serve 24/7. Source: AmeriGas

Filling an RV's built-in tank? You can't swap those. See RV fills in Utah.

Common questions

How much propane is in an exchange tank?: Blue Rhino and AmeriGas both say their exchange tanks hold 15 lb of propane, about 3.6 gallons.
How much propane does a 20 lb tank hold when refilled?: Up to about 20 lb, or roughly 4.7 gallons, since propane weighs about 4.2 lb per gallon.
Is refilling or exchanging cheaper?: Divide the exchange price by 3.6 to get the price per gallon you are really paying, then compare it with the refill price per gallon. A refill also lets you keep any propane left in your tank.