Propane Tank Exchange vs Refill: Cost per Gallon

A grill-tank exchange sells 15 pounds of propane net, which is 3.57 gallons at 4.2 pounds a gallon, while a refill of the same 20 lb cylinder to its overfill stop takes about 4.6 gallons. The exchange price divided by 3.57 is therefore the real price per gallon: a $22 swap costs $6.16 a gallon, and it beats a refill only if the refill station charges more than that.

The EIA’s survey of propane dealers puts both ends of the chain in view. For the week of October 26, 2026 it recorded a residential price of $2.730 a gallon and a wholesale price of $1.291, both excluding taxes. An exchange tank would have to sell for $9.75 to cost the same per gallon as that residential average, and for $4.61 to match wholesale. Table 3 shows how far example exchange prices sit above those two numbers. The gap is made of costs that public data cannot itemize, but it can be measured, and it is far larger than the cents that decide most arguments about which grill-tank route is cheaper.

Retailers set both prices store by store. Blue Rhino’s own FAQ answers the question of whether exchange pricing varies between retailers with “Prices for propane exchange vary by retailer, depending on the propane market, the location of the store, and other factors,” and sends the reader to the local store. Neither of the two large exchange brands publishes a national price. Every retail price in the tables below is therefore an example input, marked as one, and the formulas work with whatever number is on the rack in front of you. The ranges used, $16 to $30 for an exchange tank and $2.50 to $6 a gallon for a refill, are editorial assumptions meant to span a plausible range, with $22 as the figure used in worked lines. They are not a retailer quote or a market average.

What the 15 lb on an exchange tank means

Grill cylinders are named for what they are built to hold, not for what an exchange puts in them. Worthington Industries lists its steel 20 lb portable cylinder at a propane capacity of 4.7 gallons, a water capacity of 47.6 pounds, a nominal empty weight of 16.6 pounds, specification DOT-4BA240 and a valve with an overfill prevention device (OPD). The exchange operators state a smaller quantity. Blue Rhino says its grill tanks contain “a net weight of 15 lbs. of propane”. AmeriGas says the same of its tanks, and its terms for exchange retailers describe “20lb propane gas cylinders filled with approximately 15lbs of propane”. A tank labeled 20 lb is sold with 15.

To turn pounds into gallons, the arithmetic uses the Propane Education & Research Council’s (PERC) property table for liquid propane: specific gravity 0.504 and a weight of 4.2 pounds per gallon at 60 degrees Fahrenheit. Fifteen pounds divided by 4.2 is 3.571 gallons, which is rounded to 3.57. The same table gives total heating values of 21,548 Btu per pound and 91,502 Btu per gallon, and dividing one by the other implies 4.246 pounds per gallon, a shade above the rounded 4.2. With that figure the exchange tank would hold 3.53 gallons, 1.1 percent less, and a $22 swap would be $6.23 a gallon instead of $6.16. The choice of 4.2 does not change any conclusion here, and it is the figure PERC prints.

Measured against capacity, the exchange fill is 78 percent of the AmeriGas “when full” figure and 75 percent of the federal weight limit, so a buyer of an exchange tank pays for a cylinder whose last quarter is empty. The operators give no reason in the pages checked, and the arithmetic does not guess at one. What the arithmetic fixes is the unit price: whatever an exchange costs, it buys 3.57 gallons, and the same cylinder sold full would carry about 1.03 gallons more.

The two routes also sell different things. An exchange hands over a cylinder that has been cleaned, leak-tested and inspected, which Blue Rhino describes in its process statement, at a flat price per tank. Blue Rhino adds that it is “not a deposit program” and that the customer walks away with a tank they own, and that any standard 20 lb tank of any brand can be swapped. AmeriGas likewise accepts all brands, and says some retailers refill the customer’s own cylinder instead. A refill sells propane into a cylinder the customer already owns, priced by the gallon, by the pound or as a flat fill fee, depending on the station. The exchange price does not change with how much propane was left in the cylinder handed back, and that matters more than it looks; a later section puts numbers on it.

How a 20 lb cylinder is filled: 42 percent by weight, 80 percent by volume

Two different limits get quoted for the same cylinder, and they are not the same number. The federal one is a weight rule. Under the hazardous materials regulations, a DOT specification cylinder may be filled with propane to a maximum filling density, defined as a percent of the weight of water the cylinder would hold. For liquefied petroleum gas with a specific gravity between 0.504 and 0.510 at 60 degrees, the table in 49 CFR 173.304a(d)(1) says 42 percent. Applied to the 47.6-pound water capacity of a 20 lb cylinder, that is 19.99 pounds of propane, which matches the nameplate figure. The same section requires that the amount filled be determined by weight, and that the weight be checked on an accurate scale after the cylinder is disconnected from the filling line.

The 80 percent figure is a volume limit, and it exists because the liquid expands as it warms. PERC’s guide to dispensing propane safely says propane “expands and contracts with temperature change” and that, to allow for this, “propane containers are typically filled to 80 percent of their capacity. New portable tanks are equipped with an over-filling prevention device to limit the maximum propane level to 80 percent.” PERC adds that released liquid propane vaporizes to about 270 times its original volume, which is why the margin matters. That guide dates from 2007; the 80 percent statement also appears in the AmeriGas tank-size page, which says a propane tank “is only able to be filled to 80%”.

Why the two limits land in the same place

They are the same rule seen at different temperatures. The Occupational Safety and Health Administration’s standard for LP-gas, 29 CFR 1910.110, carries the same 42 percent in its Table H-27 and works an example: a 100-gallon water-capacity aboveground tank of propane at specific gravity 0.510, filled to 42 percent, takes 79.8 gallons, and the standard assumes the liquid sits at 40 degrees, where a gallon weighs 4.37 pounds rather than 4.2. Carry that through for a 20 lb cylinder. The Worthington cylinder’s volume of 1,318 cubic inches is 5.71 gallons. At 40 degrees, 20.0 pounds of propane occupies 4.57 gallons, or 80.2 percent of the cylinder. At 60 degrees the same weight occupies 4.76 gallons, or 83.4 percent. The 80 percent stop and the 42 percent weight limit coincide in a cool fill, and drift apart by a few percent in a warm one.

The practical reading is that a cylinder filled to its overfill stop holds somewhere between 19.2 and 20.0 pounds depending on the liquid temperature, while an exchange tank holds the operator’s stated 15. The limits are listed so the price per gallon can be read correctly, but they are not filling instructions, and nothing here substitutes for the attendant, the scale and the overfill device that make the limits work.

Weight, volume and the 60 degree gallon

Pounds and gallons are different handles on the same fuel, and a price quoted in one converts to the other only through a density. PERC’s 4.2 pounds per gallon is the density of liquid propane at 60 degrees. OSHA’s table shows 4.37 pounds per gallon at 40 degrees, 4 percent denser, because the liquid contracts as it cools. A station that sells by the gallon and a station that sells by the pound therefore describe slightly different quantities as the weather changes, and the cleanest comparison is the one used below: convert everything to the 60 degree gallon and, where heat is the point, to Btu.

Exchange tanks sidestep the issue by selling a fixed weight, which is why the conversion runs from pounds to gallons here rather than the reverse. A refill priced per pound converts with the same factor. A refill at $4 a gallon is $0.952 a pound, and an exchange at $22 is $1.467 a pound, so the exchange costs 1.54 times the refill on a per-pound basis, the same ratio as per gallon because the conversion cancels.

Dollars per gallon from an exchange price

The calculation takes one line. Divide the tank price by 3.571 gallons. Table 3 runs it for exchange prices from $16 to $30, shows the same figure per pound and per million Btu (using the EIA’s 91,452 Btu per gallon for propane), and sets each beside the EIA residential price of $2.730. The tank prices are example inputs, spaced at the kind of range a reader might see on a rack, and are not claimed prices from any retailer.

Hand check on the middle row: $22 x 4.2 = $92.40, and $92.40 / 15 = $6.16 a gallon. In heat terms, one gallon carries 91,452 Btu, so a million Btu takes 10.93 gallons, and 10.93 x $6.16 is about $67.36. The EIA residential price on the same basis is $29.85 per million Btu, so the swapped tank carries a heat price 2.26 times the bulk residential price.

The multiple column is the one to keep. At $16 a tank the gallon costs 1.64 times the residential average; at $30 it costs 3.08 times. Even the lowest example is $1.75 a gallon over the dealer price. That premium is not a scandal by itself. A residential dealer fills a tank at the house from a metered bulk truck, while a rack sells 3.57 gallons through a cashier. What the table measures is how much of the price of a grill tank is the propane and how much is everything wrapped around it: at $22, the propane at the EIA residential price is worth $9.75, or 44 percent of the price.

The refill side and the break-even price

A refill is easier to compare because it can be quoted per gallon, per pound or as a flat charge for a fill, and the quantity delivered is set by the cylinder. A cylinder filled to its overfill stop takes about 4.6 gallons, so a refill at a price of r dollars per gallon costs 4.6 x r. The break-even against an exchange follows from setting the two per-gallon prices equal: the exchange price at which a swap costs the same per gallon as the refill is 3.571 x r. Table 4 lists both for refill prices from $2.50 to $6.00.

At $4 a gallon a full fill costs $18.40, and an exchange ties at $14.29. An exchange at $22 against that refill costs $3.60 more per visit, 20 percent more, and delivers 22 percent less propane. The comparison reverses only when the refill price is high or the station charges a flat fee that does not scale. A flat fill fee of $24, for example, on a cylinder taking 4.6 gallons, is $5.22 a gallon, which is cheaper per gallon than a $22 swap but dearer than a refill priced per gallon at $4. The table is the more reliable guide because it does not assume a fee structure.

One caution on the full-fill column. It assumes the cylinder comes in empty and is filled to the stop. A cylinder that arrives with a few pounds left takes less, and a refill priced by the gallon or pound charges only for what went in. That asymmetry, between a flat exchange price and a metered refill, is the subject of the section on part-used tanks below.

Where both prices sit against the EIA propane series

Table 5 lists the EIA readings behind the comparisons. The agency collects the residential price from dealers every week from October through March and publishes it with the wholesale price as dollars per gallon excluding taxes. Our propane price explainer covers how those series are built, and the winter-by-winter propane price history places today’s reading among 36 heating seasons.

The residential price barely moved over winter 2025-26, from $2.417 to $2.678, a spread of $0.261. Over a 3.57-gallon tank that spread is $0.93. The wholesale series moved much more in relative terms, from $0.824 a year ago to $1.291 now, up 57 percent, while the residential price rose 12 percent. The year’s wholesale rise of $0.467 a gallon, passed through in full, would add $1.67 to a tank, which is 8 percent of a $22 swap. The fuel is the smaller part of what a grill tank sells, so even a large wholesale move reaches the rack price as a modest one.

The cost of an hour at the grill

A cooking hour is the unit most grill owners actually care about, and it follows from the heat in the tank. PERC’s table of approximate gas input for typical appliances, reprinted from NFPA 54, lists a barbecue at 40,000 Btu an hour. That is a maximum input, the figure printed on the grill’s data plate when every burner is on high; the actual rating of a given grill can be lower or higher, and the manual states it. At the EIA’s 91,452 Btu per gallon, a 40,000 Btu grill burning flat out uses 0.437 gallons an hour, or 1.84 pounds.

An exchange tank carries 326,614 Btu (3.571 gallons x 91,452), and a full refill of 4.6 gallons carries 420,679. Dividing by the input rate gives hours of burner time at full input. Table 6 does it for four input ratings and prices the hour three ways: from an exchange tank at $22, from a refill at $4 a gallon, and from propane bought at the EIA residential price. The price columns are examples, and the hour counts are ceilings.

At the 40,000 Btu rating, the exchange tank lasts 8.2 hours and a full refill 10.5 hours; the fuel for an hour costs $2.69 from the exchange tank, $1.75 from the refill, and $1.19 at the bulk residential price. The difference between the exchange and the refill is $0.94 an hour, which is under a dollar at this rating. Fuel is a small cost of grilling at any of these prices; what the exchange premium changes is the annual total for a heavy user.

Real use sits below the maximum. If a grill held at medium or with one burner off draws half the rated input, the hours per tank double and the cost per hour halves. The tables above are ceilings on consumption, not predictions, and a reader who knows the average setting can scale every row. For a season view, suppose 100 hours of burner time at an average input of 20,000 Btu an hour, an illustrative load. That is 2.0 million Btu, or 21.9 gallons. It takes 6.1 exchange tanks, or 4.8 full refills. At $22 a tank the exchange route costs $134.72 for the season; refilling at $4 a gallon costs $87.48; the same gallons at the EIA residential price would cost $59.70. The gap between the first two is $47.24 a season on those inputs. Our heating fuel comparison per million Btu puts a gallon of propane beside oil, gas and electricity on the same scale.

What a part-used tank does to the exchange price

The flat exchange price assumes the customer brings back an empty cylinder. Many do not. A grill owner who swaps at the first sign of the gauge dropping, or who keeps a spare and rotates, hands back a cylinder that still holds propane, and that propane goes with it. The cost per gallon of the propane actually gained is the price divided by the net gallons, which is the 15 lb received less the pounds returned, over 4.2.

Returning a cylinder with 3 pounds left lifts a $22 swap from $6.16 to $7.70 a gallon, an increase of 25 percent for nothing but timing. A refill priced by the gallon or pound has no such penalty, because the pump counts only what goes in. That is the one place where a refill’s advantage is structural and not a matter of this week’s prices. A refill station that charges a flat fee regardless of the amount added would reintroduce the penalty, so the pricing basis is worth asking about.

Knowing what is left takes a scale. A cylinder’s weight when empty is its tare weight; Worthington lists a nominal 16.6 pounds for its 20 lb steel cylinder, and the marked figure on any particular cylinder can differ by manufacturer. A cylinder at 31.6 pounds on a bathroom scale is a new exchange tank by that nominal tare; one at 21.6 pounds has about 5 pounds left, enough for roughly 2.7 hours at the 40,000 Btu rating if the heat is 21,548 Btu a pound. Weighing is information about the tank, not an instruction to fill it.

Cylinder age, carrying and the cases where swapping makes sense

A refill needs a cylinder that is legal to fill, and that is where an exchange earns its price for many owners. Portable propane cylinders are DOT specification cylinders, and the regulations require periodic requalification. For a DOT 4B, 4BA, 4BW or 4E cylinder with a corrosion-resistant coating that is used only for non-corrosive gas, 49 CFR 180.209(e) allows volumetric expansion testing every 12 years in place of the standard five. Paragraph (g) lets a 4BA cylinder in liquefied petroleum gas service take an external visual inspection instead of a hydrostatic test when requalification falls due, with later inspections at five-year intervals. AmeriGas summarizes the practical effect as requalification “between 5 and 12 years based on the date of manufacture”, with the manufacture date stamped into the collar, and says that an exchanged tank “has already been recertified”. Blue Rhino says it requalifies tanks when needed and retrofits tanks with outdated components.

The cost of that process is not in the price per gallon, and it is not published in the sources checked. For an owner of an old cylinder with no recent requalification mark, a swap replaces the cylinder and its paperwork in one transaction; a refill of that cylinder may be declined if it is out of date. Blue Rhino’s FAQ also notes that, under the NFPA 58 code as it describes it, only tanks with overfill protection devices can be refilled, effective April 1, 2002, a rule Blue Rhino says dozens of states have adopted as law. The code text itself is behind NFPA’s access wall and was not read, so that point rests on the operator’s statement.

Two further cases favor the swap on grounds other than fuel cost. The first is time and distance: a refill location that is miles out of the way adds a cost that the price per gallon does not show. AmeriGas lists 24-hour self-serve exchange kiosks and says it has over 54,000 locations nationwide; Blue Rhino says about 65,000 retail locations. The second is a second cylinder. A household that keeps a spare can swap the empty at leisure, which turns the part-used penalty above into a small one if the spare is rotated only when truly empty. Neither case changes the arithmetic of the gallon; both change what the gallon is for.

Getting the cylinder home

AmeriGas’s transport guidance, repeated on its exchange page, is to keep a filled cylinder upright and secured so it cannot fall, shift or roll, to close the valve, to use a plug if the retailer requires one, to carry it in a ventilated part of the vehicle, never to leave it in a hot vehicle, and to take it out on arrival. The same advice applies whichever route supplied the tank. A refill adds a little more propane to carry, 4.6 gallons against 3.57, and the cylinder is correspondingly heavier by about 4.3 pounds at the stated fills.

A one-line test, and what it leaves out

The test is a single division: exchange price over 3.57, compared with the refill price per gallon. If a $22 swap is across the street from a refill at $4 a gallon, the refill wins on fuel cost by $2.16 a gallon, and by $3.60 on a full tank even after allowing for the extra propane it delivers. If the nearest refill is a flat fee, divide the fee by the gallons it buys before comparing. If the cylinder is older than its requalification date, the refill may not be available at all, and the swap is the legal route.

What the test leaves out is everything a price list leaves out. Local sales tax is not in the EIA’s figures, which exclude taxes, and it varies by state and county. The EIA also publishes regional and state residential prices in the same weekly release, and a reader far from the national average should use the local series. The retail inputs here are examples because no operator or EIA series publishes them, and a reader who photographs the rack price and the refill price on the same day will have better data than any table here.

For the wider picture of why a gallon of propane costs what it does at each step from the Gulf Coast hub to the home tank, the propane price explainer follows the chain, the 500-gallon tank guide follows the same fuel into a household that buys it by the truckload, and the fuel types hub collects the other fuel-substitution questions on this site.

Data and sources, all checked November 3, 2026: U.S. Energy Information Administration, Weekly Heating Oil and Propane Prices (release of October 28, 2026), with the weekly histories for residential propane and wholesale/resale propane; EIA, British thermal units (propane 91,452 Btu per gallon). Propane Education & Research Council, Propane Technical Pocket Guide (Tables 1A and 3A) and Dispensing Propane Safely into Agricultural Equipment (2007; 80 percent fill and overfill device). 49 CFR 173.304a and 180.209 as published in the eCFR (text as of October 1, 2026). Occupational Safety and Health Administration, 29 CFR 1910.110, Storage and handling of liquefied petroleum gases (Table H-27 and paragraph (b)(19)). Worthington Industries, portable propane cylinders sheet (March 2025) and steel portable cylinders specification sheet (water capacity and cylinder volume). Blue Rhino, How much propane does Blue Rhino put in its tanks?, Does exchange pricing vary greatly between retailers?, Is Blue Rhino a deposit program?, the overfill protection device answer and How to Exchange a Propane Tank. AmeriGas, Buy, Exchange, or Dispose of Your Propane Tank, Propane Tank Sizes, Cylinder Exchange Terms and Conditions, Propane Tank Recertification and Transporting Propane Tanks. Conversions, break-even prices, hours per tank and percentage changes follow from the cited quantities.