Gas Pipe Sizing Calculator
Enter the appliance demand and the measured run, add your elbows, tees and swept bends, and get the smallest copper tube that carries the gas within the 1 mbar drop BS 6891 allows between the meter and the appliance.
Enter the appliance demand and the measured pipe run to size it.
Natural gas only, against BS 6891 Table 1 (1 mbar maximum loss, meter outlet to appliance inlet). Between published lengths this takes the next longer entry rather than interpolating, so it never overstates the gas available. A design aid — it does not replace the standard.
BS 6891 allows a maximum 1 mbar pressure loss between the meter outlet and any appliance inlet at design maximum flow. Fittings count: add 0.5 m for each elbow and tee (1 m at 35 mm) and 0.3 m for each swept bend, then read the table against that effective length. Where a run falls between published lengths this takes the next longer entry rather than interpolating — the discharge curve is convex, so a straight line between two points would overstate the gas available.
Reference
BS 6891 Table 1 (copper tube to BS EN 1057, relative density 0.6)