Propane Tank Refill vs Exchange Cost Calculator
Propane refill and exchange costs: the practical difference
A propane cylinder that is running low gives you two familiar choices. You can take your own cylinder to a refill station and pay for the fuel pumped into it, or you can hand it to an exchange rack and pay one posted price for another cylinder. The exchange is often faster, particularly when a convenience store is open after a refill station has closed. However, its flat price can hide two important differences: any propane in the returned cylinder is surrendered, and the replacement cylinder may not contain as much propane as a full refill.
This calculator compares the money paid today with the propane actually gained. It is designed for the common nominal 20-pound grill cylinder, but the fields also work for larger portable cylinders. Enter the capacity, your local refill price, the exchange price, the amount an exchanged cylinder contains, and your estimate of fuel remaining. The result separates the smaller immediate bill from the lower cost per usable gallon, because those answers can differ.
A full nominal 20-pound cylinder generally holds about 4.7 gallons of propane. Many exchange programs provide about 15 pounds of fuel, or approximately 3.5 gallons. That one-gallon-plus difference is why comparing only two shelf prices can be misleading. A $17 exchange may be less cash than a full refill from an empty tank, yet still cost more for each gallon you receive.
How to use the propane tank refill versus exchange calculator
Start with the capacity printed or known for your cylinder. The default 4.7 gallons is appropriate for a typical 20-pound barbecue cylinder at its usual safe fill level. Next, enter the refill station’s posted per-gallon price and the exchange cage’s flat fee. Keep the exchange-fill field at 3.5 gallons unless your local supplier states a different propane weight or gallon amount.
The most useful input is the propane remaining in the tank you would return. A collar gauge is only an estimate, so use it as a guide rather than a precise measurement. If practical, weigh the cylinder and subtract the tare weight stamped beside TW on its collar. Divide the remaining propane weight by roughly 4.24 pounds per gallon. You may also add a refill-trip cost for driving, tolls, parking, or the value you put on an extra errand. Leave that field at zero when the refill stop is already on your route.
After selecting Compare options, read the result in two ways. “What you pay” is the immediate outlay. “Cost per usable gallon” divides that outlay by the new propane available for future cooking. The scenario table then shows how the decision changes from an empty tank through a full one, while the chart plots the same crossover visually.
The propane refill, exchange, and break-even formulas
For a refill, the station adds the difference between cylinder capacity and the propane left in it. The refill bill is that missing volume multiplied by the refill price, plus any trip cost:
In contrast, the exchange price remains fixed even when the returned tank contains fuel:
In these formulas, V is capacity in gallons, L is leftover propane, Pr is the refill price per gallon, Pe is the exchange fee, and T is the refill-trip cost. Setting the immediate costs equal gives the same-tank break-even leftover:
If your remaining fuel is above that break-even amount, refilling is the lower bill today. If it is below that amount, exchanging is the lower bill today. This threshold does not mean both choices leave you with the same fuel supply; it simply compares the two payments.
Cost per usable gallon reveals the fuel lost in a swap
To compare the value received, divide each option’s cost by the propane gained. Refilling adds V − L gallons, so its effective price is:
An exchange sets the returned cylinder aside and gives you an exchange fill level E. The usable gain is only E − L gallons:
When the propane remaining approaches the exchange fill amount, the exchange gives you very little additional fuel for the full flat fee. If your cylinder already contains more than an exchange cylinder would, a swap leaves you with less propane than you brought in. The calculator labels that outcome as “no gain” instead of presenting an artificial price per gallon.
Worked propane example: a partly full 20-pound grill tank
Suppose a 4.7-gallon cylinder has 2.0 gallons left. A refill station charges $4.25 per gallon, an exchange costs $17.00, and the exchange cylinder holds 3.5 gallons. With no travel cost, the refill adds 2.7 gallons and costs 2.7 × $4.25, or $11.48. The exchange costs $17.00, but replacing a 2.0-gallon cylinder with a 3.5-gallon cylinder produces only 1.5 usable new gallons.
In that example, refilling is cheaper at the counter and costs $4.25 per usable gallon. The exchange works out to about $11.33 per usable gallon. The owner also gives up propane worth $8.50 at the refill price. Even if the exchange rack is convenient, the calculation makes the trade-off visible instead of treating the original tank as empty.
Now consider an empty cylinder. A full 4.7-gallon refill would cost $19.98 at the same price, compared with a $17.00 swap. The exchange saves $2.98 in immediate spending, but supplies only 3.5 gallons at about $4.86 per gallon. In other words, the exchange can be sensible when time matters or the tank is empty, while still carrying a higher fuel price.
Real-world propane tank choices beyond the price board
Convenience is a legitimate part of the decision. Exchange cages may be available late at night or on holiday weekends, while refill service has limited hours and can require an attendant. Exchanges also move an old cylinder out of your hands. If your tank is corroded, damaged, or past its requalification date, an exchange may provide value that a simple fuel-price comparison cannot capture.
On the other hand, refilling a sound, current cylinder generally preserves its fuel, gives you the higher fill level, and avoids needless cylinder transport. Keeping a second in-date cylinder is often the simplest way to avoid a rushed choice. Use one cylinder while the other is full, then refill the empty one during a normal errand rather than swapping a partly full tank before guests arrive.
Fuel estimates are imperfect. Propane volume changes with temperature, actual exchange fills can vary, and prices can change by season and location. The calculator is a planning tool, not a fuel-safety device. Keep cylinders upright, outdoors, away from ignition sources, and follow the supplier’s instructions for transport and inspection. Never attempt to transfer propane between consumer cylinders without proper equipment and training.
Propane refill and exchange questions
Is refilling always cheaper?
Not always as an immediate payment. A nearly empty cylinder can be exchanged for less than the cost of filling it to 4.7 gallons. Refilling usually wins once meaningful fuel remains because it preserves that propane and charges only for the missing amount.
How can I estimate propane remaining?
Use a cylinder gauge for a rough indication, or weigh the tank and subtract the tare weight marked TW. Dividing propane weight by about 4.24 gives an approximate gallon amount. Enter a conservative estimate if you are unsure.
Why is an exchange tank often not full?
A nominal 20-pound cylinder can hold about 20 pounds of propane, near 4.7 gallons. Many exchange services package roughly 15 pounds, near 3.5 gallons, while using a similar-looking cylinder and one flat exchange price.
What standards support the default capacity?
The default reflects a common 20-pound propane cylinder filled within applicable safety limits. OSHA LP-Gas requirements, NFPA 58 guidance, cylinder markings, and local supplier practices all matter; consult your supplier for the actual cylinder and exchange-fill specifications in your area.
Sources for propane capacity and safe cylinder handling
The calculator uses 4.7 gallons as a practical full-fill estimate for a nominal 20-pound cylinder and 4.24 pounds per gallon as an approximate liquid-propane conversion at 60 °F. For safety and regulatory details, consult OSHA LP-Gas requirements, NFPA 58, PHMSA cylinder guidance, and Propane Education & Research Council safety information. Local regulations and cylinder-label instructions take priority.