Propane Tank Calculator
Running out of propane mid-evening is avoidable. Most buyers discover the problem at the end of a session instead of before it because they never calculated how many hours their appliance actually pulls from a tank. This propane tank size calculator fixes that. Enter your BTU rating, tank size, and current fill level, and it returns gallons per hour, total runtime, and sessions per tank before you light the next fire.
The propane calculator covers propane fire pits, gas fire tables, gas patio heaters, and any appliance with a rated BTU output. The BTU presets auto-fill common appliance ratings so you can run the estimate in under a minute.
Propane Tank Calculator
Enter BTU and tank size for runtime, sessions per tank, and refill cost
Your Appliance
50,000
Your Tank
100%
Optional: Session & Cost
Enter 0.25 to 24 hours.
Your Results
–
Gallons Per Hour
–
Hours of Runtime
At current fill level
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Gallons Available
Cost per hour of use –
Full refill cost (at current price) –
Running at medium flame reduces BTU output by 30 to 50 percent, extending runtime proportionally without a noticeable drop in flame height for most fire pit and fire table applications.
How the Propane Tank Calculator Works
Every propane tank calculator runs on one constant: according to the U.S. Department of Energy Alternative Fuels Data Center, one gallon of liquid propane contains 91,502 BTU of usable energy. This figure is fixed by the physical properties of propane and does not change by brand, supplier, or temperature.
The calculation is: BTU rating divided by 91,502 equals gallons consumed per hour. A 50,000 BTU appliance burns 0.546 gallons per hour. Divide total gallons in the tank by the hourly consumption rate and you get runtime in hours.
The fill-level slider adjusts the calculation for partial tanks. If your dial gauge reads 40 percent, set the slider to 40 and the calculator uses only the available propane, not the full tank capacity. This is the most useful function for an evening where the tank is not fresh.
Sessions per tank uses floor division: if a tank provides 8.7 hours and sessions run 2 hours each, the result is 4 full sessions, not 4.35. A partial session is treated as zero because an unfinished tank means a refill is needed before next time.
BTU Output Reference by Appliance
Use this table if the BTU label on your appliance is worn or missing.
| Appliance | Typical BTU Range | Gallons Per Hour | 20 lb Tank Runtime |
|---|---|---|---|
| Gas fire pit (mid-range) | 40,000–60,000 | 0.44–0.66 | 7.2–10.8 hr |
| Gas fire table | 55,000–90,000 | 0.60–0.98 | 4.8–7.9 hr |
| Standard patio heater | 30,000–46,000 | 0.33–0.50 | 9.5–14.3 hr |
| High-BTU patio heater | 46,000–65,000 | 0.50–0.71 | 6.7–9.5 hr |
| Large fire pit | 60,000–100,000 | 0.66–1.09 | 4.3–7.2 hr |
| Gas grill (medium) | 25,000–40,000 | 0.27–0.44 | 10.8–17.5 hr |
| Camping / tabletop stove | 8,000–12,000 | 0.09–0.13 | 36–52 hr |
All figures assume full-output operation. Runtime increases significantly at medium or low flame.
Worked Examples
Example 1: Fire Pit, 20 lb Tank, 2-Hour Sessions
Appliance: 50,000 BTU propane fire pit · Tank: 20 lb (4.73 gallons), full
Gallons per hour: 50,000 ÷ 91,502 = 0.546 gal/hr
Runtime: 4.73 ÷ 0.546 = 8.7 hours
Sessions at 2 hours each: floor(8.7 ÷ 2) = 4 sessions
Cost at $4.00/gallon: 4.73 × $4.00 = $18.92 per full tank
Four two-hour evenings from a single 20 lb tank. A spare tank in rotation covers any session that runs longer than planned.
Example 2: High-BTU Fire Table, 100 lb Tank, 3-Hour Sessions
Appliance: 65,000 BTU gas fire table · Tank: 100 lb (23.6 gallons), full
Gallons per hour: 65,000 ÷ 91,502 = 0.710 gal/hr
Runtime: 23.6 ÷ 0.710 = 33.2 hours
Sessions at 3 hours each: floor(33.2 ÷ 3) = 11 sessions
Cost at $3.50/gallon: 23.6 × $3.50 = $82.60 per full tank
Eleven three-hour sessions from a 100 lb tank at $7.51 per session. At the same per-gallon price, five 20 lb exchanges would deliver fewer total hours and cost more per gallon due to the 15 lb exchange fill.
Example 3: 1 lb Tank, Camping Stove
Appliance: 10,000 BTU tabletop stove · Tank: 1 lb (0.236 gallons), full
Gallons per hour: 10,000 ÷ 91,502 = 0.109 gal/hr
Runtime: 0.236 ÷ 0.109 = 2.16 hours, or approximately 2 hours 10 minutes at full output
Reduce flame to low and runtime extends to 3 to 4 hours. One-pound tanks are best suited to short cooking tasks, not extended heating sessions.
Reading Your Propane Tank Gauge
20 lb cylinders do not include a built-in gauge. The most reliable method is weight: an empty cylinder weighs approximately 17 lb (the tare weight is stamped on the collar). Subtract 17 from the total weight to get current propane pounds.
30 lb, 40 lb, and 100 lb tanks include a dial gauge reading 0 to 100 percent. At 80 percent the tank holds its rated propane volume, as tanks fill to 80 percent maximum by code for thermal expansion. Most suppliers schedule refill when the gauge reads 20 to 30 percent.
Set the fill-level slider in the calculator above to your current gauge reading before each session. A propane tank cover with a gauge window lets you check levels without removing the cover, which matters for fire tables with enclosures.
Choosing the Right Tank Size
Run this propane calculator with your specific BTU rating before committing to a tank size. A 20 lb cylinder covers casual outdoor use: two to four sessions per week at a mid-BTU fire pit or patio heater is manageable with one tank and one spare. It is the default choice because it fits the enclosures built into most fire tables and is available for exchange at hardware stores and gas stations nationwide.
A 100 lb tank becomes the better option when the appliance runs three or more sessions per week, BTU output exceeds 65,000, or the tank is plumbed to a fixed outdoor installation. Direct refills at a propane dealer typically cost less per gallon than exchange programs, and the savings compound at higher volume.
For buyers running both a fire pit and a patio heater on the same evenings, run the calculator for each appliance separately and add the hourly figures. Combined use often makes a 100 lb tank the more practical choice for a full season.
If you are planning a DIY fire pit build, the fire pit block calculator covers the masonry side. For a fire-pit-specific fuel breakdown with seasonal totals and per-week propane usage summaries, the propane usage calculator at the link above covers those extended planning outputs in detail.
Frequently Asked Questions
How long does a 20 lb propane tank last on a fire pit?
Twenty pounds of propane holds 4.73 gallons. A 50,000 BTU fire pit consumes 0.55 gallons per hour, giving roughly 8.6 hours at full output. At medium flame, burn rate drops 30 to 50 percent. Enter your BTU into the propane tank calculator for your exact sessions per tank.
How long does a 1 lb propane tank last?
One-pound tanks hold 0.236 gallons of propane. A 10,000 BTU camp stove burns through a 1 lb cylinder in approximately 2 hours and 10 minutes at full output. Adjusting to low flame extends runtime to 3 to 4 hours, depending on the appliance and ambient temperature.
How do I read a propane tank gauge?
Dial gauges on tanks 30 lb and larger show percentage remaining, not gallons. At 20 percent, most suppliers require a minimum delivery. For a 20 lb cylinder, weigh it: an empty tank weighs 17 lb. Subtract 17 from the total weight to get current propane weight in pounds.
What does a propane tank refill cost?
Refill pricing at most propane dealers runs between $3.00 and $5.00 per gallon. A 20 lb tank holds 4.73 gallons, putting a full refill at $14 to $24 depending on location. Exchange programs at hardware stores typically cost $25 to $30 but fill tanks to only 15 lb, not 20.
What size propane tank do I need for a fire pit?
Most backyard fire pits run on a 20 lb cylinder, which provides 8 to 14 hours of runtime depending on BTU rating and flame setting. Buyers running three or more sessions per week, or operating above 60,000 BTU, typically find a 100 lb tank more cost-efficient over a full season.
How much propane does a fire pit use per hour?
Propane consumption equals BTU rating divided by 91,502, the energy content of one gallon of propane in BTU. A 50,000 BTU fire pit burns 0.55 gallons per hour. A 70,000 BTU fire table burns 0.77 gallons per hour. Running at medium output cuts either figure by 30 to 50 percent.
Final Thoughts
The propane tank calculator above returns runtime, sessions, and cost from a single BTU input. Use the fill-level slider before any outdoor session to confirm the tank on hand will last the evening. For buyers choosing between tank sizes, the sessions-per-tank output makes the math direct: match the tank size to the number of sessions you run per refill cycle, not to the hours on the label.
For buyers still selecting an appliance, the full fire pit catalog at Fire Pit Surplus includes BTU specs on every product page for easy input into this calculator. Smokeless fire pits are an alternative for buyers who want a contained outdoor fire without propane supply management.
