Gas Pipe Sizing Calculator — What Size Gas Pipe Do I Need?

This calculator determines the required gas pipe diameter based on the total gas load (kW), the effective pipe run length (including fittings allowance), and the pipe material. It uses simplified sizing tables derived from BS 6891.

The method

1. Calculate effective pipe length: Actual length + (elbows × 0.5m) + (tees × 1.0m)

2. Look up pipe diameter from the sizing table for the given kW load and effective length, ensuring the pressure drop does not exceed 1 mbar.

Fittings equivalents

• Elbow (90°): 0.5m equivalent pipe length
• Tee: 1.0m equivalent pipe length

Common pipe sizes

• 15mm copper: Suitable for small loads up to ~20 kW over short runs
• 22mm copper: Most common domestic size, suitable for up to ~30-50 kW
• 28mm copper: Required for higher loads or longer runs, up to ~70-100 kW
• 35mm copper: Large domestic or light commercial loads

Standards

Gas pipe sizing must comply with BS 6891 (Installation and maintenance of low pressure gas pipework of up to 35mm on premises) and IGE/UP/2 (Gas installation pipework, boosters and compressors on service pipes). All gas work must be carried out by a Gas Safe registered engineer.