Size the drain flow rate above the total output of the shower, not equal to it. A standard shower head is roughly 0.2–0.3 L/s; a rain shower 0.4–0.6 L/s; add the flows together if the shower has multiple outlets. Level-access showers need extra margin because water spreads across the floor rather than being contained.
Typical shower outputs
| Fixture | Approximate flow |
|---|---|
| Standard shower head | 0.2–0.3 L/s |
| Rain shower head (200–300 mm) | 0.4–0.6 L/s |
| Large rain head (300 mm+) | 0.6 L/s and above |
| Body jets (per set) | Add to the shower head flow |
| Hand shower + rain head together | Add both |
Manufacturers publish flow rates at a given head of water — typically 20 mm. Compare like with like when comparing products from different suppliers.
Why the margin matters
- Level-access showers — with no threshold, water spreads across the whole floor. If the drain cannot keep up, water reaches the doorway.
- Hair and soap build-up — a drain running at its limit blocks quickly as debris accumulates between cleans.
- Simultaneous use — two people showering, or a rain head plus hand shower, doubles the load.
What reduces actual flow rate
- Long horizontal outlet runs with insufficient fall
- Multiple bends in the waste pipe
- A shallow channel body that limits water depth over the outlet
- A tile-insert grate, which lets water in around the edges rather than through a wide grille
Practical selection
For a standard shower, a drain rated well above the head output is sufficient. For rain showers, large openings or commercial projects, specify the drain against the calculated total and confirm the outlet route allows the stated flow.
Send us your shower specification and we will confirm the required capacity. Request a Quote