Measure the internal diameter of the pipe below the grate — not the grate, and not the bowl. That single measurement decides which seal fits. The grate is always wider than the pipe beneath it, and the wider upper part of the trap is not the reference either. This is why people most often order a size too large.
The job takes a minute: lift the grate, measure the pipe wall to wall through the centre, and find the range in the table below.
How to measure, step by step
- Lift the grate. Most lift out with a screwdriver or release with a single screw.
- Look into the pipe. There is often a bowl below the grate that narrows — the narrower part below it is what matters.
- Measure the internal diameter wall to wall, through the centre. A tape, a caliper or the measuring tag all work.
- Note it in millimetres and find the size whose range contains your figure.
If you fall between two sizes, take the smaller one. The silicone ribs expand and seal against the pipe wall; a seal that is too large will not go in, while a slightly smaller one still holds.
Size table
| Measured | Size | Typical use |
|---|---|---|
| 32 mm | 1.25″ | Offices, ice machines, cold rooms |
| 38 mm | 1.5″ | Domestic bathrooms, baths |
| 50–58 mm | 2″ | Hotel bathrooms, hospitals |
| 55–65 mm | 2.5″ | Older buildings |
| 75–85 mm | 3″ | Professional kitchens and hotels |
| 80–89 mm | 3″/3.5″ | Refurbished hospitals, projects |
| 89–100 mm | 3.5″ | Industrial kitchens, bakeries |
| 88–102 mm | 3.5″/4″ | Food processing |
| 102–110 mm | 4″ | Meat processing, breweries, wineries |
| 120–135 mm | 5″ | Garages, plant rooms |
| 150–156 mm | 6″ | Shipyards, terminals |
The most common size in commercial buildings is 3″, around 75 mm. In domestic bathrooms it is usually 1.5″. Prices by size are in the catalogue.
Round, square and channel drains
The seal fits into the pipe, not the grate, so the shape of the grate is not an obstacle. It suits round and square floor drains, gullies and channel drains — the only requirement is a round pipe below for the seal to sit in. With a square grate you still measure the pipe underneath.
If you are not sure
Two options. The measuring tag is a keyring with the ranges for every size — hold it against the opening and read off the size, no arithmetic. Or send us a photograph of the drain with something of known size beside it for scale, such as a coin, and we will say which size applies.
For buildings with many drains of different diameters it usually makes sense to measure a few representative ones and order in groups rather than one by one.
Fitting, once you have chosen
No tools and no work on the pipework: lift the grate, drop the seal into the pipe, replace the grate. About 30 seconds per drain. Nothing is glued and nothing is cut, so the seal can be taken out again — that is what the extraction tool is for.