Formula Used
Equivalent gallons = entered fuel converted into gallons.
Stored BTU = equivalent gallons × BTU per gallon.
Usable BTU = stored BTU × efficiency × usable fuel factor.
Adjusted load = appliance BTU/h × appliance count × duty cycle.
Runtime = usable BTU ÷ adjusted load.
Fuel per hour = adjusted load ÷ useful BTU per gallon.
Target fuel = adjusted load × target hours ÷ useful BTU per gallon, adjusted for reserve.
How to Use This Calculator
Enter the LP fuel amount and choose the matching unit. Use pounds for common cylinders. Use gallons for bulk tanks.
Set the BTU per gallon and density. The default values are suitable for many propane planning estimates.
Enter appliance input, count, duty cycle, efficiency, reserve, runtime target, and price. Press Calculate.
Review usable energy, runtime, hourly fuel draw, total cost, cost per hour, and fuel required for your target runtime.
Example Data Table
| Fuel Case |
Fuel Amount |
Appliance Load |
Efficiency |
Estimated Use |
| Grill cylinder |
20 lb |
30,000 BTU/h |
80% |
Short event cooking |
| Shop heater |
100 lb |
60,000 BTU/h |
82% |
Temporary heating |
| Bulk tank |
120 gal |
90,000 BTU/h |
85% |
Longer building load |
LP BTU Planning Guide
What This Calculator Does
LP fuel is often measured in gallons, pounds, liters, kilograms, or vapor cubic feet. Appliances are usually rated in BTU per hour. This calculator connects those units. It estimates total heat energy, usable heat after efficiency losses, practical runtime, fuel cost, and fuel needed for a target runtime.
Why BTU Planning Matters
A BTU is a unit of heat energy. LP systems use BTU ratings to size tanks, burners, heaters, generators, and cooking equipment. A small appliance can run for many hours from a single cylinder. A large heater can empty the same cylinder quickly. Accurate planning helps you avoid outages, undersized storage, and costly emergency refills.
Useful Advanced Inputs
The form includes custom fuel values because real LP mixes and supplier data can vary. Propane is commonly estimated near 91,500 BTU per gallon. Density is often near 4.24 pounds per gallon. You can edit both values. Efficiency reduces delivered heat, so an 80 percent appliance does not deliver every stored BTU. Duty cycle is also important. A heater rated at 30,000 BTU per hour may not fire continuously all day.
How Results Help
The output separates stored BTU from usable BTU. Runtime shows how long the entered fuel can support the appliance load. Fuel per hour explains consumption in gallons. Cost per hour helps compare appliances or operating schedules. Target fuel shows how much LP is needed for a chosen number of hours while keeping your reserve setting.
Practical Use Cases
Use this tool for patio heaters, standby generators, furnaces, shop heaters, food trucks, cabins, and temporary jobsite heat. It also helps compare cylinder sizes. For example, a 20 pound cylinder contains less usable heat than a 100 pound cylinder, but it is easier to move. Large tanks support longer loads but need delivery access.
Record actual refill dates and meter readings. Those notes improve future estimates and reveal unusual consumption patterns quickly.
Planning Tips
Always keep a reserve. Cold weather can reduce vaporization performance. Regulators, hoses, altitude, and appliance condition may change real output. Treat the result as a planning estimate, not a safety approval. For permanent fuel systems, confirm sizing with the appliance manual, supplier guidance, and local code requirements.
FAQs
1. What does LP mean?
LP usually means liquefied petroleum gas. In many fuel planning cases, it refers mainly to propane. Some supplies may include blends, so editable heat values are included.
2. What BTU value should I use for propane?
A common planning value is 91,500 BTU per gallon. Supplier data, fuel composition, and measurement method can vary. Use your supplier value when available.
3. Why does efficiency lower the result?
Appliances do not convert every stored BTU into useful heat. Efficiency accounts for flue losses, mechanical losses, or other delivery losses.
4. What is duty cycle?
Duty cycle is the percent of time the appliance runs at rated input. A heater cycling half the time can use less fuel than one running continuously.
5. Why include reserve fuel?
Reserve fuel protects against unexpected demand, refill delays, cold weather, and gauge error. It also keeps planning more conservative.
6. Can this size my permanent gas system?
Use it for estimates only. Permanent systems need proper pipe sizing, regulator checks, appliance manuals, and local code review by qualified professionals.
7. Why are pounds and gallons both supported?
Small cylinders are often sold by pounds. Bulk tanks are often planned in gallons. The calculator converts both using the density input.
8. Does cold weather change runtime?
Cold weather may reduce vaporization and available delivery rate. Stored BTU may be similar, but appliance performance can suffer without correct tank sizing.