Manhole Size Calculator
Enter the depth from ground to the bottom of the pipe and the largest pipe diameter. The calculator suggests an inspection chamber or a man-entry manhole, its internal size, the cover and the rings you need.
- Depth and pipe size
- Chamber or manhole
- Cover and rings
Depth to invert is from the finished ground to the bottom inside of the outgoing pipe.
Shallow drains need a small chamber, deep ones a manhole you can climb into. Below about 1.5 metres, someone has to go down to clear a blockage, so the chamber becomes a manhole at least 1,200 mm across. Bigger pipes need wider manholes for the channels.
Manhole size chart
Typical UK sizes. Search for a size.
| Depth (m) | Pipe (mm) | Chamber | Internal size (mm) |
|---|---|---|---|
| Up to 0.6 | 100 | Inspection chamber | 450 |
| Up to 1.0 | 150 | Inspection chamber | 600 |
| Up to 1.5 | 150 | Inspection chamber | 1000 |
| Over 1.5 | 150 | Manhole | 1200 |
| Any | 450 | Manhole | 1350 |
| Any | 600 | Manhole | 1500 |
| Any | 900 | Manhole | 2100 |
Your water company's rules take priority on public sewers.
Depth and chamber
150 mm pipe. Slide the depth.
The section shows the chamber rings, the cover and the pipe through the base.
How to choose a chamber
Depth, then pipe. Step through it.
Depth
To the invert.
Every bend, junction and change of gradient in a drain needs a chamber so it can be rodded.
Plastic, precast concrete or brick
Chamber types. Compare them.
Light, quick to fit.
Concrete sections.
Built in place.
Covers are graded by load: light for gardens, heavier for drives and roads.
Before ordering
Drain checks. Tick each item.
Tick each item as you go.
Deep chambers are confined spaces. Never go in without gas testing and a trained team.
What you get
Chamber sizing. Each tile explains one result.
Type and size.
How many.
Size.
To invert.
Ladder or not.
Inspection chambers in gardens can usually have light covers. Drives need covers rated for cars.
Frequently Asked Questions
No question matches that search.
What size manhole do I need?
At least 1,200 mm across for man entry, more for pipes larger than 375 mm.
When do I need a manhole instead of an inspection chamber?
Usually when the drain is deeper than about 1.5 metres.
What is the depth to invert?
From the ground to the bottom inside of the outgoing pipe.
How big should a manhole cover be?
At least 600 × 600 mm clear opening for man entry.
Can I use a plastic inspection chamber?
Yes, for shallow private drains, usually up to about 1.2 metres.
How many rings does a manhole need?
About one 500 mm ring for every half metre of depth, plus a cover slab.
Do deep manholes need ladders?
Yes, with rest platforms on very deep ones.
Access to your drains
Choose the chamber from the depth and pipe size, fit the right cover and keep every bend and junction reachable for rodding.
More size calculators
Each one has its own calculator, worked examples and answers to common questions.