RM postcode district map, Chigwell
Supplier statuses last checked .
The RM postcode area covers 20 districts and 10,007 live postcodes, from RM1 to RM20. It is centred on Chigwell and also covers Brentwood, Grays, Dartford, Tilbury and Swanscombe.
Districts here average 500 postcodes.
Where the RM districts sit
2 districts are plotted without a label where labels would overlap; every one is in the table below.
Where RM sits
It falls across Greater London, Thurrock and Essex.
Water supply across RM
All 20 RM districts are supplied by Thames Water. That makes RM simple in a way many areas are not: one company, one set of rules, one status to check.
Thames Water has a hosepipe ban in force from 23 July 2026, covering the whole of RM.
The shape of the RM area
RM3 is the largest district with 923 postcodes around Brentwood, and RM19 the smallest with 143. The area divides into 66 postcode sectors.
Several districts share a settlement, which is a common source of confusion when a form rejects an address: RM1, RM4, RM5, RM6, RM7, RM8, RM9 and RM10 all point at Chigwell, RM2, RM3, RM11, RM12 and RM14 all point at Brentwood and RM15, RM16 and RM17 all point at Grays.
What borders RM
RM sits next to DA (Dartford) to the south, IG (Chigwell) to the west, E (City of London) to the west, SE (City of London) to the south west and BR (Swanley) to the south west.
RM districts, settlements and water supply
Principal settlement is the town or city each district sits in or nearest to, derived from OS Open Names. It is not the Royal Mail post town, which is licensed data and not published openly. Status is resolved live from each company’s own notice.
Water hardness in RM
No water company covering RM publishes hardness figures as open data. The gap is named per district below so you know who to ask.
| District | Hardness | As published | Supply zone | Published by |
|---|---|---|---|---|
| RM1 | Not published by Thames Water. Check with your supplier. | |||
| RM2 | Not published by Thames Water. Check with your supplier. | |||
| RM3 | Not published by Thames Water. Check with your supplier. | |||
| RM4 | Not published by Thames Water. Check with your supplier. | |||
| RM5 | Not published by Thames Water. Check with your supplier. | |||
| RM6 | Not published by Thames Water. Check with your supplier. | |||
| RM7 | Not published by Thames Water. Check with your supplier. | |||
| RM8 | Not published by Thames Water. Check with your supplier. | |||
| RM9 | Not published by Thames Water. Check with your supplier. | |||
| RM10 | Not published by Thames Water. Check with your supplier. | |||
| RM11 | Not published by Thames Water. Check with your supplier. | |||
| RM12 | Not published by Thames Water. Check with your supplier. | |||
| RM13 | Not published by Thames Water. Check with your supplier. | |||
| RM14 | Not published by Thames Water. Check with your supplier. | |||
| RM15 | Not published by Thames Water. Check with your supplier. | |||
| RM16 | Not published by Thames Water. Check with your supplier. | |||
| RM17 | Not published by Thames Water. Check with your supplier. | |||
| RM18 | Not published by Thames Water. Check with your supplier. | |||
| RM19 | Not published by Thames Water. Check with your supplier. | |||
| RM20 | Not published by Thames Water. Check with your supplier. | |||
Hardness is published per census area, not per postcode, so these figures characterise a district rather than measuring one address. They are a scale and taste matter, not a safety one. Hardness data version wessex-water@2022-2025+yorkshire-water@2026.
Download the RM data
No signup, no email wall. GeoJSON carries the district points, the supplier and the live status, so it can be dropped straight into a map.
District positions are averaged postcode centroids from OS Code-Point Open. They show roughly where a district sits, not where its boundary runs, and are not legal boundaries.
Frequently asked questions
How many postcode districts are in the RM area?
There are 20 RM postcode districts, running from RM1 to RM20, and they contain 10,007 live postcodes across 66 sectors.
What towns does the RM postcode area cover?
RM covers Chigwell, Brentwood, Grays, Dartford, Tilbury and Swanscombe. The area takes its name from Chigwell, and each district is listed with its settlement in the table on this page.
Which water company supplies RM postcodes?
Thames Water supplies all 20 RM districts. Supply boundaries follow the pipe network rather than postcode geography, so confirm against your water bill if you are near the edge of the area.
Why do RM1 and RM4 both say Chigwell?
RM1, RM4, RM5, RM6, RM7, RM8, RM9 and RM10 all serve Chigwell, covering different parts of it. A single town routinely needs more than one postcode district once it passes a few thousand delivery points, so this is normal rather than an error in an address.
Can I download a free RM postcode map?
Yes. This page offers the RM districts as GeoJSON, CSV and SVG, free and with no signup or email address required. The GeoJSON carries each district's position, its water company and its current restriction status, so it can be dropped straight into a mapping tool.
Why is the RM area called Chigwell when it covers Brentwood?
RM takes its letters from Chigwell, where the sorting office that served the area was based when the code was allocated. Brentwood is the largest settlement in the area today, in RM3, but the area code follows the historic sorting geography rather than current population.
Which councils cover the RM postcode area?
RM reaches into Greater London, Thurrock and Essex. A postcode area is not a council area: they were drawn for different purposes and a single district can sit across a council boundary, so your postcode does not tell you which authority you pay.