Tightness test calculator

The permissible pressure drop is read from the installation volume and the fuel gas, not the meter size. Any perceptible movement, even within limits, must be proved not to come from the pipework by isolating the appliances and retesting with no movement allowed. Purge volume is 1.5 × IV on every job, so the IV is worked out every time. Natural gas may be tested at 18 mbar where 20 cannot be reached, with IGEM/G/13 checks to follow. Gas Safe Register recommends recording which edition was used.

From 1 October 2026. Edition 4 was published in March 2026, both editions ran together for six months, and Edition 3 is withdrawn on 30 September 2026.

With existing appliances connected and no smell of gas: natural gas 8 mbar up to 0.005 m³, 4 mbar to 0.010 m³, 2.5 mbar to 0.015 m³ and 1 mbar to 0.035 m³; LPG/Air 1.5 mbar to 0.025 m³ and 0.5 mbar to 0.035 m³; LPG 2, 1 and 0.5 mbar to 0.0025, 0.005 and 0.01 m³, then no perceptible movement. Pipework only, or new appliances: no perceptible movement at all. A smell of gas fails the test whatever the gauge shows.

0.25 mbar or less on a water gauge or an electronic gauge reading to two decimal places; 0.2 mbar or less on an electronic gauge reading to one decimal place.

Add the internal volume of every run of pipe (length × the volume per metre for its size), add the valves and fittings (10% of the pipework volume unless you calculate the actual volume), and add the meter: 8 litres for a U6 or G4, 2.4 litres for an E6, 25 litres for a U16 or G10. Divide litres by 1000 for m³. For hidden pipework assume the largest size you can see.

No. The calculation runs entirely in your browser. Nothing you enter is sent to a server or saved. Manifold customers get the same calculator on the check page, where the result is saved against the job and printed on the Landlord Gas Safety Record.