LP Gas Line Size Calculator

Calculator Inputs

Connected appliance load BTU per hour

Propane heat value BTU per cubic foot

Diversity factor Percent of load expected to run

Reserve factor Percent added for future load

Straight pipe run Feet

Pipe material

Specific gravity Propane vapor is commonly near 1.52

Inlet pressure Inches water column

Allowed pressure drop Inches water column

Vertical rise Feet upward

90 degree elbows

Tees

Valves

Regulators or restrictions

Equal branch count

Project note

Example Data Table

Example	Load	Run	Fittings	Allowed drop	Typical planning result
Outdoor grill and small heater	100,000 BTU/h	40 ft	3 elbows, 1 valve	0.5 in. w.c.	Often near 1/2 in steel
Range and water heater	180,000 BTU/h	65 ft	5 elbows, 1 tee, 1 valve	0.5 in. w.c.	Often near 3/4 in steel
Generator branch	325,000 BTU/h	90 ft	6 elbows, 2 tees, 2 valves	0.5 in. w.c.	Often near 1 in steel

Formula Used

Design load = connected load × diversity factor × reserve factor.

Gas flow = design load ÷ propane heat value.

Equivalent length = straight run + fitting allowance.

Pressure drop estimate = K × SG × L × Q^1.82 ÷ ID^4.8655 + elevation allowance.

In this calculator, K is a low pressure planning constant. SG means specific gravity. L means equivalent length. Q means cubic feet per hour. ID means inside diameter.

How to Use This Calculator

Enter the total connected propane appliance load.
Keep the default heat value, or enter your supplier value.
Add a diversity factor if every appliance will not run together.
Add a reserve factor for future appliance capacity.
Enter the pipe run, fittings, material, and pressure limits.
Press the calculate button.
Review the result shown above the form.
Download the CSV or PDF for planning records.

LP Gas Line Planning

LP gas line sizing starts with connected appliance load. Each burner, heater, or generator needs vapor at a steady pressure. A pipe that is too small can starve the appliance. It can also create nuisance shutdowns, yellow flames, and poor recovery. A pipe that is too large costs more, but usually performs better. The right choice balances load, distance, pressure drop, and local rules.

Why Equivalent Length Matters

Gas does not only lose pressure in straight pipe. Elbows, tees, valves, unions, and regulators create resistance. Designers convert those fittings into added pipe length. This calculator adds fitting allowances to the entered run. The total is called equivalent length. It gives a more realistic pressure loss estimate than straight distance alone.

How Flow Is Estimated

Appliance load is entered in BTU per hour. The tool divides that load by propane heat content. Standard propane vapor is often estimated near 2,516 BTU per cubic foot. The result is cubic feet per hour. A diversity factor can reduce the design load when all appliances will not run together. A reserve factor can increase the load for future growth.

Pressure Drop and Pipe Choice

The sizing check uses a low pressure gas flow relationship. Flow increases strongly with inside diameter. Pressure loss increases with length and flow rate. The tool tests common pipe sizes for the selected material. It selects the smallest size that stays within the allowed pressure drop.

Important Safety Notes

This page is for planning, budgeting, and early comparison. It is not a code approval. Final work should follow the fuel gas code used in your area. A licensed professional should confirm regulator capacity, tank pressure, venting, supports, burial depth, shutoff valves, and appliance instructions. Never use an online estimate as the only sizing document. Propane work needs careful testing before service.

Using the Results

Read the recommended nominal size first. Then review calculated flow and pressure loss. If the result is close to the limit, choose a larger size. Also check the longest branch, not only the main run. Real systems may include regulators, sediment traps, flexible connectors, and manifolds. Those items can change performance. Keep records for the installer and inspector during final review later.

FAQs

What does this LP gas line size calculator do?

It estimates a propane vapor pipe size from load, pipe length, fittings, gas properties, and allowed pressure drop.

Can this calculator replace a licensed design?

No. It is only a planning tool. A qualified installer must confirm final sizing, code rules, regulator capacity, and appliance requirements.

What is equivalent length?

Equivalent length combines straight pipe distance with extra resistance from elbows, tees, valves, regulators, and similar fittings.

Why is BTU per hour required?

BTU per hour shows the appliance fuel demand. The calculator converts that demand into propane vapor flow.

What propane heat value should I enter?

A common planning value is 2,516 BTU per cubic foot. Use your local supplier value when available.

Why does pipe material matter?

Pipe materials have different inside diameters and resistance behavior. CSST should always be checked against manufacturer sizing tables.

What if no pipe size passes?

Increase pipe size, reduce equivalent length, reduce load, allow more pressure drop, or use a different regulator design.

Should I include future appliances?

Yes. Add reserve capacity when future appliances are likely. It may prevent costly pipe replacement later.