Refill vs. exchange: the 15 lb vs. 20 lb math
This is the fact that drives most of the comparison — and it is printed on the exchange cage in small type, if anywhere.
The core fact
A standard “20 lb” grill tank holds about 4.7 gallons of propane when full.
Exchange cages typically fill that tank to only 15 lb — roughly 3.5 gallons — while charging a flat price presented as the price of a 20 lb tank.
So at an exchange, you pay the 20 lb price for 15 lb of propane: 25% of the tank's capacity never reaches your grill.
What that does to your price per gallon
Work it backwards from any flat exchange price. If a swap costs $X, your effective price per gallon is $X ÷ 3.5 gal — not $X ÷ 4.7. A refill, by contrast, is priced openly per gallon and fills the whole 4.7 gallons, so the comparison is direct:
Verified refill example — Ace Hardware, Anderson, CA: $2.98/gal (source: propanepricetracker.com, Shasta County tracker, checked Oct 2026).
Full 20 lb refill = 4.7 gal × $2.98 = $14.01, for the full 20 lb.
Orlando-area U-Haul example range: $3.95–$4.25/gal (Oct 2026).
Full refill = $18.57–$19.98, for the full 20 lb.
Hold any exchange cage's flat price next to those totals — remembering the cage gives you 15 lb, not 20 lb — and divide it by 3.5 gallons, not 4.7, before comparing. One documented example: a Rochester, NY hardware chain publishes refill at $14.96 for a 20 lb tank against $24.49 for an exchange (checked Oct 2026). Most cages publish no refill figure at all, so compare your local numbers directly.
Why the spread between refill stations also matters
Choosing which refill station matters too: a $1/gal spread between two stations is worth about $4–$5 on every 20 lb fill. Propane is a repeat purchase — monthly to seasonal for most households — so a better per-gallon price compounds all year. That is why this site tracks per-gallon prices by city instead of just listing stations: see the price index.
When exchange still makes sense
- Your tank is damaged, rusty, or past its recertification date — exchange it for a certified tank rather than refilling it. See tank recertification & expiry.
- You need propane outside refill-station hours and convenience outweighs cost, once.
- Your tank is an odd size a local refill station cannot fill.
For a sound, in-date tank, refill wins on math almost every time.
Keep your tank, keep the savings
One more advantage of refilling: you keep your own tank, whose condition and history you know, instead of trading it for whichever tank the cage hands you. Check prices near you: California · Florida · National index.