Gas Pipe Sizing Calculator (BTU Load + Equivalent Length)

How to Use This Gas Pipe Sizing Calculator

1. Select the gas type. Choose Natural Gas (NG) or Liquid Propane (LP). Propane has higher energy density per cubic foot, so LP capacities are scaled 1.60× above the natural gas IFGC Table 402.4(1) baseline for the same nominal pipe size and equivalent length.
2. Enter connected appliance BTU loads. Add each gas appliance on the branch run with its input rating in BTU/hr — furnace, water heater, range, dryer, fireplace, or boiler nameplate values. Use Add Appliance for multiple connected loads; the calculator sums total demand automatically.
3. Enter straight pipe length and fitting counts. Measure the developed straight run in feet, then count 90° elbows, 45° elbows, straight-run tees, and 90° branch tees. Each fitting adds equivalent length per IFGC practice: 90° = 5 ft, 45° = 3 ft, straight tee = 1 ft, branch tee = 5 ft.
4. Review recommended nominal pipe size. Live Results show the smallest black iron pipe size whose table capacity meets total BTU demand at the computed equivalent length. Total connected load and equivalent length are displayed for field verification.
5. Check the flow compliance badge. Green means safe margin under the code chart. Yellow warns when utilization exceeds 90% — consider upsizing if future appliances are likely. Red indicates demand exceeds 2" low-pressure chart capacity; split branches or move to a 2 PSI regulated system.

Formulas & Example

Equivalent Length (ft) =
  Straight Pipe
  + (90° Elbows × 5)
  + (45° Elbows × 3)
  + (Tees Straight × 1)
  + (Tees Branch × 5)

Total BTU Load = Σ Appliance Input Ratings
LP Capacity = NG Table Value × 1.60

Select smallest nominal pipe where Table Capacity ≥ Total BTU Load

Equivalent Length = 40 + (3 × 5) + (1 × 5) = 60 ft → use 60 ft table column
3/4" at 60 ft = 137,000 BTU/hr ≥ 100,000 BTU/hr

Result: 3/4" Black Iron Pipe — ~73% utilization (compliant)

Frequently Asked Questions