What does it cost to fill a 20 lb propane tank?
One multiplication answers it — as long as you know your local per-gallon price, which is exactly what this site exists to publish.
The formula
A 20 lb tank holds about 4.7 gallons when full.
Fill cost = 4.7 × price per gallon
Note the assumption: a refill fills the tank you bring. If your tank still has propane in it, you pay only for the gallons added — another refill advantage over a flat exchange price.
Worked examples (verified prices only)
| Example | Price/gal | Math | Full 20 lb fill | Source |
|---|---|---|---|---|
| Ace Hardware — Anderson, CA | $2.98 | 4.7 × $2.98 | $14.01 | propanepricetracker.com (Shasta County tracker), checked Oct 2026 |
| U-Haul locations — Orlando area (aggregate range, not a single station) | $3.95–$4.25 | 4.7 × $3.95–$4.25 | $18.57–$19.98 | U-Haul location pages in Oct 2026 search results |
We deliberately do not publish a “national average fill cost” here: an average built from unsourced numbers would be exactly the kind of figure this site refuses to invent. Your cost is your city's verified price × 4.7.
Why the spread matters
Every $1/gal of price spread moves a 20 lb fill by about $4–$5 — that is the arithmetic. The spread we have actually verified is smaller: U-Haul's own Orlando-area pages ranged from $3.95 to $4.25/gal, a $0.30/gal spread within one metro, worth about $1.40 on a 20 lb fill. So checking before you drive is worth real money over a season of refills.
Compare against exchange correctly
An exchange tank typically contains 15 lb (≈3.5 gal), not 20 lb. To compare fairly, divide the exchange's flat price by 3.5 to get its effective $/gal, then compare with your refill station's $/gal. Full explanation: Refill vs. exchange.
Find your number
Check the price index for a verified price near you — or report the price you paid so your city has one.