Tightness Test Calculator (beta)
Enter the installation volume and your gauge readings to get the maximum permissible pressure drop under IGEM/UP/1B Edition 4, and whether the test passes. Edition 4 changed the basis: the allowance comes from the volume of the installation, not the badged capacity of the meter.
Beta — not yet reviewed by a qualified engineer.Detail
Works to IGEM/UP/1B Edition 4, mandatory from 1 October 2026 — Edition 3 sets the permitted drop from the meter badged capacity instead, so it gives a different answer. The Edition 4 figures are transcribed from a published secondary source rather than a licensed copy of the standard — check them against your own copy before you rely on them. Tell us if something is wrong.
Enter the installation volume to get the maximum permissible pressure drop.
The PDF is a calculation record, not a certificate — it carries no declaration and no signature.
Method and standard
What changed in Edition 4
The permitted drop now comes from the installation volume, not the badged capacity of the meter. Two jobs on the same U6 can be allowed different drops, which under Edition 3 they could not. Run the same figures through both editions and they disagree, so work to one or the other and know which.
The natural gas bands
- Up to 0.005 m³ — 8 mbar
- Over 0.005 up to 0.010 m³ — 4 mbar
- Over 0.010 up to 0.015 m³ — 2.5 mbar
- Over 0.015 up to 0.035 m³ — 1 mbar
LPG and LPG/air have tighter bands of their own, and the top LPG band allows no perceptible movement at all.
Perceptible movement, as a number
Edition 4 stopped leaving this to the eye. On a water gauge or a standard electronic gauge it is 0.25 mbar; on an electronic gauge reading to one decimal place it is 0.2 mbar. Pick your gauge and the calculator uses the right one.
Used in
- Installation volume calculator — work out the volume first.
- Domestic testing & purging record — where the allowable drop and the readings are recorded.
Method
Permitted drop is banded by installation volume — natural gas allows 8 mbar to 0.005 m³, 4 mbar to 0.010, 2.5 mbar to 0.015 and 1 mbar to 0.035. LPG and LPG/air have their own bands.
Reference
IGEM/UP/1B Edition 4, mandatory from 1 October 2026; Edition 3 set the permitted drop from the meter badged capacity instead, so the two disagree on the same job. Covers domestic natural gas, LPG and LPG/air up to 0.035 m³ — above that the test belongs to IGEM/UP/1A or UP/1. The 2 minute test period and the 10 litre / 4 mbar pair are as described in BS 6891:2015 Annex C.2 e).
Related calculators
- Gas Rate Calculator — Convert meter readings to m³/hr and kW for natural gas or LPG.
- Flue-Gas Ratio Checker — Get the CO/CO₂ combustion ratio and its BS 7967 action band.
- Gas Pipe Sizing Calculator — Size a whole installation against BS 6891:2015, section by section.
- Installation Volume Calculator — Work out installation volume the Edition 4 way — pipework, meter and fittings.