Calculator inputs
Use the fields below to estimate propane needed and total refill cost.
Example data
These examples show typical gardening-related propane usage scenarios.
| Use case | Tank (lb) | Current % | Target % | Price/gal | Fees | Tax % | Notes |
|---|---|---|---|---|---|---|---|
| Patio heater for evening gardening | 20 | 15 | 80 | 4.25 | 0.00 | 0 | Quick top-up before a weekend session. |
| Weed torch for hardscape edges | 30 | 40 | 90 | 4.60 | 2.50 | 5 | Includes a small flat service fee. |
| Greenhouse heater backup cylinder | 40 | 10 | 85 | 4.10 | 4.00 | 8 | Budgeting for winter plant protection. |
Formula used
1) Convert tank capacity to gallons
Tank gallons = Tank pounds ÷ (pounds per gallon)
2) Find the refill percentage change
Refill % = max(0, Target % − Current %)
3) Compute propane needed
Gallons needed = Tank gallons × (Refill % ÷ 100)
Pounds needed = Gallons needed × (pounds per gallon)
4) Compute cost
Subtotal = Gallons needed × Price per gallon
Taxable = Subtotal + fees
Tax = Taxable × (Tax % ÷ 100)
Total = Taxable + Tax
How to use this calculator
- Enter your tank capacity in pounds (e.g., 20 lb cylinder).
- Set your current and target fill percentages.
- Add your local price per gallon.
- Optionally include fees and a tax rate.
- Press Calculate cost to see results above the form.
- Use the download buttons to save CSV or PDF.
Safety note: refill policies and maximum fill levels vary. Confirm local rules and use proper storage for garden equipment and propane cylinders.
Why refill accuracy matters for garden heat tools
Patio heaters, weed torches, and greenhouse burners often run near 30,000 to 45,000 BTU per hour. One gallon of propane provides about 91,500 BTU, so a 20 lb cylinder (about 4.7 gallons at 4.24 lb/gal) can cover roughly 9 to 14 hours of burn depending on the appliance. Estimating refill cost prevents weekend work from stopping unexpectedly mid-task during long outdoor sessions.
Interpreting tank size, pounds, and gallons
Cylinders are labeled in pounds because that is the propane mass when full. Retail prices are often by gallon, so the calculator converts pounds to gallons using a pounds-per-gallon factor. A common reference is 4.24 lb/gal near mild temperatures. If your supplier meters by liter, use gallons as a consistent comparison volume for quotes.
Using current and target fill percentages
The refill volume is driven by the difference between current and target percentages. For example, moving from 25% to 80% uses 55% of the cylinder’s volume. On a 30 lb tank, that is about (30 ÷ 4.24) × 0.55 ≈ 3.9 gallons. This approach matches how top-offs are billed when a cylinder is weighed or metered during filling.
Fees, tax, and the true cost per gallon
Flat fees can change the effective price more than the posted per-gallon rate, especially for small top-ups. The calculator adds service and other fees, then applies tax to the combined taxable amount. The “effective cost per gallon” output helps choose between a quick stop refill and a scheduled delivery, because it normalizes the total cost against the propane volume.
Budgeting scenarios for gardening seasons
For frost protection, a greenhouse heater may run nightly for weeks. If you estimate 2 gallons per night, a 40 lb cylinder (about 9.4 gallons) lasts roughly 4 nights. Multiply expected nights by your effective cost per gallon to forecast a seasonal budget. For weed torch work, plan short bursts: refilling to 90% before major edge cleanup avoids downtime and reduces last-minute premium fees.
FAQs
1) Why does the calculator ask for pounds per gallon?
Propane is sold by volume, but cylinders are rated by pounds. Pounds per gallon converts tank size into gallons so price-per-gallon totals stay consistent across suppliers and tank sizes.
2) What if my supplier charges per liter?
Use the gallons needed as your target volume, then convert to liters if you want. One gallon is about 3.785 liters, so multiply gallons by 3.785 for an approximate liter estimate.
3) Can I estimate cost for a partial top-off?
Yes. Enter your current percentage and the target percentage you want to reach. The calculator prices only the volume required to cover that difference, plus any fees and tax.
4) Does the result include fees and tax?
It can. Add service fees, other fees, and a tax rate if they apply. The estimate shows a subtotal, taxable amount, tax value, and the final total so you can compare options.
5) Why is 80% a common target?
Many filling practices leave headspace for temperature expansion. Your local rules and cylinder type may differ, so treat the percentage as a planning number and follow supplier safety limits.
6) How can I reduce refill costs?
Compare effective cost per gallon, not just posted price. Larger fills dilute flat fees. Keeping a spare cylinder for garden heaters or torches also avoids urgent refills with higher premiums.