A flow rate is only a figure when the pressure it was measured at is printed next to it. The same shower head is honestly around 9 l/min at 3 bar and roughly 5 l/min at 1 bar, and a listing prints the larger one.
Why pressure changes everything
Flow through a fixed set of holes rises with pressure. A maker measures at a reference pressure — 3 bar is the usual one in European specifications — and publishes what came out. Your bathroom has whatever pressure it has, which depends on the supply, the height of the floor and what else is running.
What this means when comparing two products
Two heads quoted at 9 l/min and 12 l/min are only comparable if both were measured at the same pressure. When one states its pressure and the other does not, the honest comparison is between the one that states it and nothing.
The minimum that matters more
Several products state a minimum operating pressure rather than a flow: thermostatic cartridges and large rain heads both do. That figure is not marketing. Below it a thermostatic valve regulates badly, and a large head drips rather than rains.
This does not replace the manufacturer's own instructions. Every dimension, thread size, flow rate, operating pressure, water seal depth and load figure on this page is reported from the manufacturer's own documentation, with its unit written as published, and named as such — none of it is measured here. A flow rate is reported with the pressure the manufacturer measured it at, and is never converted to another pressure, because no conversion exists.
Questions people actually ask
How do I find out my own water pressure?
A pressure gauge that screws onto a tap or a washing-machine valve costs very little and reads it directly. Your water supplier also publishes a typical pressure for the network, though the pressure at your shower depends on your own pipework and floor.
Is a lower flow rate always worse?
No. A well-designed 6 l/min head can feel stronger than a poorly designed 12 l/min one, because how the flow is grouped matters as much as how much of it there is. What is misleading is a figure with no pressure attached.
Last reviewed 5 September 2026