The answer in two lines
A floor drain is not chosen by grate size alone. The size (10x10, 15x15 or 20x20 cm) is the cover you see on the floor, but the flow rate is set by the outlet pipe diameter underneath, and smells are stopped by the water seal (trap), which the European standard EN 1253-1 sets at a depth of at least 50 mm. Pick the size by the space (small bathroom, large shower or kitchen) and leave final measurements to your plumber.
"Should the floor drain be 10x10 or 15x15? And why does the smell come back from the drain?" It is asked in every bathroom and kitchen fit-out, and the drain is fixed at first-fix, before tiling, so changing it later means breaking tiles. In this guide from Tawredaat (توريدات), an electrical and finishing materials store in Cairo and Giza, we compare the common sizes, explain how to stop smells, and give installation rules, with figures from standards and well-known manufacturers' catalogs.
What types of floor drains are there?
- Pop-up drain: the cover opens and closes with a simple action, so you close it when not in use and open it for showering or washing. All the Plaza models we stock are of this type.
- Fixed grate drain: a fixed perforated cover that lets water through all the time and needs cleaning from time to time.
- Material: the Plaza product pages on our site say the Cart and Crystal Touch models are stainless steel, the Silver 20x20 has a stainless finish, and the Silver 10x10 and 15x15 have a silver finish and 1.25 mm thickness.
10x10, 15x15 or 20x20: which suits you?
No standard says "this bathroom needs this drain", so this table is a practical suggestion from Tawredaat by space, not a code figure:
| Size | Suitable space | Note |
|---|---|---|
| 10x10 cm | Small bathroom, balcony, lightly used kitchen | Smallest grate, least visible on the floor |
| 15x15 cm | Standard bathroom, shower area and kitchen | The most common, and the most versatile choice |
| 20x20 cm | Large shower, laundry, or a spot where a lot of water collects | Larger grate, easier to clean |
Grate size does not set the flow rate
Data sheets from the German maker Dallmer show that drainage depends on the outlet diameter (DN) more than on the cover size, with figures tested to EN 1253 at a 20 mm water level:
| Drain (Dallmer) | Outlet | Flow rate | Water seal depth |
|---|---|---|---|
| 100x100 mm frame (517012) | DN 50 | 0.92 l/s | 50 mm |
| 150x150 mm frame (551252) | DN 50 / DN 70 | 0.80 l/s | 50 mm |
| 150x150 mm frame (571274) | DN 100 | 1.40 l/s | 50 mm |
- ✔ So a 150x150 drain with a DN 70 outlet flows 0.80 l/s, a smaller 100x100 drain with DN 50 flows 0.92, and the 150x150 drain with DN 100 reaches 1.40.
- ✔ In the American MIFAB catalog, a shower head is given as an example demand of 5 GPM (about 0.32 l/s by conversion), and it says the maximum flow depends on the depth of the drain, the outlet size and the free area of the grate.
- ⚠ These are Dallmer figures only, not Plaza. The Plaza product pages on our site do not state the outlet diameter or the water seal depth, so ask your plumber to confirm the right outlet for your drain pipe.
How do you stop floor drain smells?
The smell is sewer gas coming up when there is no water seal, or when the seal has dried out. The fixes:
- ✔ A water seal (trap): the European standard EN 1253-1 covers trapped floor gullies with a water seal of at least 50 mm. The International Plumbing Code (IPC, Section 1002.4) says each fixture trap has a liquid seal of 2 to 4 inches (51 to 102 mm).
- ✔ The seal can evaporate: IPC Section 1002.4.1 says trap seals subject to evaporation must be protected with a water-supplied primer or a barrier-type device. So for a drain you rarely use (guest bathroom or balcony), make sure it holds water and pour water in from time to time.
- ✔ Close the pop-up cover when not in use, which cuts insects and smell coming from the opening and makes cleaning easier.
- ⚠ No water seal means the smell comes back whatever the size or type of the drain. This is the first thing to ask your plumber before buying.
How is a floor drain installed correctly?
- ✔ Slope the floor toward the drain: according to the Ceramic Tile Foundation, plumbing code requires a shower floor slope of a quarter inch per foot (about 2%, or 2 cm per metre by conversion) so the water reaches the drain.
- ✔ Drain level with the tiles: the drain should be the lowest point of the floor, with its cover flush with the finished tiles, after allowing for adhesive and tile thickness.
- ✔ Location: at the lowest point, away from the walking path where possible, and in the shower, where the water collects.
- ⚠ The drain pipe must be connected to the water seal before plaster and tiles, because changing it afterwards means breaking tiles.
Common mistakes when choosing a floor drain
- ⚠ A drain higher than the floor: water collects around it instead of flowing in.
- ⚠ Installing before the slope is set: the wrong slope leaves standing water even with a large drain.
- ⚠ Choosing the size by looks only: a large drain on a small pipe will not flow more than the pipe itself.
- ⚠ Forgetting to clean it: hair and soap block the grate, so choose a drain whose cover opens easily and clean it regularly.
Finally, installing the drain and deciding the outlet diameter and slope should be left to a skilled plumber / qualified plumbing technician who sees the drainage on site.
Floor drains available on Tawredaat
These Plaza models are available to buy now on the site:
- Plaza Silver: 10x10 cm · 15x15 cm · 20x20 cm
- Plaza Cart (stainless): 15x15 cm · 20x20 cm
- Plaza Crystal Touch (stainless, touch pop-up): 15x15 cm · 20x20 cm
You can see every model in our drains and covers collection. And if you are fitting out the whole bathroom, see our angle valve vs concealed valve guide, bathroom basin guide and rain shower vs regular shower guide.
Frequently asked questions
What size is a bathroom floor drain?
The common sizes are 10x10, 15x15 or 20x20 cm, all available on Tawredaat. The choice depends on the space, but the real flow is set by the outlet pipe diameter, not the cover size (Dallmer).
What causes floor drain smell?
Usually there is no water seal, or the seal has dried out. EN 1253-1 requires a seal of at least 50 mm, and the IPC requires 2 to 4 inches and asks for seals subject to evaporation to be protected.
Does a bigger drain flow faster?
Not necessarily. In Dallmer data sheets, a 100x100 drain with a DN 50 outlet flows 0.92 l/s and a 150x150 drain with DN 70 flows 0.80, while a 150x150 with DN 100 reaches 1.40.
What slope should the floor have toward the drain?
According to the Ceramic Tile Foundation, plumbing code requires a shower floor slope of a quarter inch per foot, about 2%.
Is a pop-up drain better than a standard one?
A pop-up closes when not in use, which reduces smell and insects coming from the opening, but it does not replace the water seal below it.
How do I find the outlet diameter of Plaza drains?
The product pages do not state it, so ask your plumber to confirm the right outlet for your drain pipe before installation.
Ready to choose the right floor drain?
Browse the floor drains available on Tawredaat in 10x10, 15x15 and 20x20 cm, with delivery in Cairo and Giza.
About Tawredaat: Tawredaat (توريدات) is an Egyptian supplier of electrical and finishing materials and sanitary ware, serving homeowners, companies and contractors in Cairo and Giza. Questions? See our FAQ.
