Channel Drain Calculator
Contact Us
Channel Drain Calculator
Count the channel lengths, gratings, end caps, corners, outlets and sump units for a linear channel-drain (ACO-style) run, and check the flow your channel must carry. Load classes and products to BS EN 1433.
Channel run components
Enter the run and its features — the tool works out how many channel units and accessories to order.
Flow the channel must carry
Peak run-off from the area draining to the channel = area × rainfall intensity. Use it to pick a channel size from the manufacturer's hydraulic chart.
Channel hydraulic capacity depends on the channel width, depth and any built-in fall, so it is product-specific — match this flow to the manufacturer's capacity chart. As a rule of thumb, more outlets or a wider/deeper channel are needed as the flow rises.
Reference & load class
Load classes (BS EN 1433) and what each component does.
| Class | Test load | Typical use |
|---|---|---|
| A15 | 15 kN | patios, pedestrian-only |
| B125 | 125 kN | domestic driveways, footways |
| C250 | 250 kN | car parks, forecourts, kerbsides |
| D400 | 400 kN | roads, HGV yards |
| E600 | 600 kN | industrial / heavy goods areas |
| F900 | 900 kN | docks, ports, airfields |
Components. Channel units (the run); gratings/covers (separate or integral); end caps (closed ends); end or bottom outlets (connect to the pipe); corner/junction units (direction changes); sump/silt units (a catchpit with a basket at the outlet). Allow leveling feet, fixing clips and sealant per the manufacturer.
Good practice. Channel drains across a driveway should fall to at least one outlet; long runs need more than one. Keep the channel below the surrounding surface so water runs in. For trafficked installations, bed and haunch the channel in concrete to the load class. ("ACO" is a brand; any BS EN 1433 channel system works the same way.)
This channel drain calculator counts the channel units, gratings, end caps, corners, outlets and sump units for a linear channel-drain run, and checks the flow the channel must carry. Load classes and products follow BS EN 1433. For the wider duty to manage surface water on site, see the Approved Documents for drainage.
Component take-off for a run
Enter the total run length, the channel unit length (most systems are 1.0 m, some 0.5 m), how the run is topped (separate gratings, gratings per metre, or integral), and the number of end caps, outlets, corners and silt traps. The calculator returns how many channel units and accessories to order — the schedule you need to price or procure the run.
Picking the right load class
The load class is set by where the channel sits, from A15 for a patio up to F900 for docks and airfields, under BS EN 1433. A domestic driveway is typically B125; a car park or forecourt C250; an adoptable road or HGV yard D400. Specifying below the trafficking load is a common and expensive mistake.
Checking the flow the channel must carry
The calculator also checks the catchment flow against the channel, so you can confirm the chosen channel width and outlet spacing will actually take the runoff rather than overtopping in a storm.
Further reading: keeping drains clear to prevent surface water flooding · drainage information needed for planning permission · the Approved Documents
Frequently asked questions
Divide the run length by the unit length, then add accessories. The calculator does this and totals the gratings, end caps, corners, outlets and sumps.
A domestic driveway taking cars is normally B125. Heavier use — forecourts, car parks, roads — steps up to C250, D400 and beyond under BS EN 1433.
Where the channel's capacity would otherwise be exceeded. The flow check helps you place enough outlets so the run drains without overtopping.
One of our experienced Flood Risk Consultants will get back to you within 60 minutes