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Calcimator

Gas Pipe Sizing Calculator

Size natural gas piping using the longest run method with Weymouth formula per IFGC standards.

Inputs

BTU/hr
ft
psi

IFGC §404 / NFPA 54: residential meter outlet 0.25 psi (7" WC); low-pressure <2 psi; medium 2–5 psi

Results

Required Pipe Size

1 inches

Pipe Capacity

335,889 BTU/hr

Pressure Drop0.01 psi
Gas Velocity10.19 fps
How to Use This Calculator
  1. Enter the total BTU load — sum the input ratings of all gas appliances (furnace, water heater, range, dryer).
  2. Enter the longest pipe run in feet from the meter to the farthest appliance.
  3. Set the inlet pressure (typically 0.25 PSI for residential, 2 PSI for medium-pressure systems).
  4. Leave specific gravity at 0.60 for natural gas, or adjust for propane (1.52).
  5. Review Required Pipe Size and verify that the calculated pressure drop stays within the allowable limit.

What each input means

Total BTU Load
Total connected gas load from all appliances (furnace, water heater, range, dryer, etc.).
Longest Pipe Run
Length from the gas meter to the farthest appliance. Used for pressure drop calculation.
Inlet Pressure
Gas pressure at the meter outlet per IFGC (International Fuel Gas Code) §404.1 and NFPA 54. Residential service: 0.25 psi (7" WC) at meter outlet typical; low-pressure systems <2 psi; medium-pressure: 2–5 psi distribution.
Gas Specific Gravity
Specific gravity of the gas relative to air. Natural gas ≈ 0.60, propane ≈ 1.52.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Total BTU Load = 200000, Longest Pipe Run = 60, Inlet Pressure = 0.5, Gas Specific Gravity = 0.6 = 4 input(s) provided
  2. Calculate Required Pipe Size
    Required Pipe Size
    1 = 1
  3. Calculate Pipe Capacity
    Pipe Capacity
    335889 = 335889
  4. Calculate Pressure Drop
    Pressure Drop
    0.009 = 0.009
  5. Calculate Gas Velocity
    Gas Velocity
    10.19 = 10.19

Engine last updated . Checked against 1 independently-derived test — how we verify calculators.

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