Dado and Picture Rail Calculator
How much dado rail or picture rail do you need? The usual sum takes the doors off the perimeter and can leave you short. Enter your room, doors and windows, and the calculator works out which openings actually reach the rail's height, splits the rest into runs, and cuts every piece from 2.4m lengths with offcuts reused.
Last reviewed: 30 September 2026
Room
Rail
Changing the rail or wall height fills in Skirting World's height: wall height divided by 5 then doubled for a dado rail, wall height minus 400mm for a picture rail. You can type your own.
Doors and Windows
Position is from the left end of the wall as you face it, to the edge of the opening (not the architrave). Walls go round the room: 1, 2, 3, 4.
How Much Dado Rail Do I Need?
The usual answer is the room's perimeter less the doors, divided by the rail length. It can leave you short. For a 4.0m × 3.5m room with one door and a window whose sill is above the rail, it gives 6 rails of 2.4m, but the room needs 7. In the table below the usual sum is short in 1 of 6 rooms.
A rail cannot bend round a corner, so every wall is its own run, broken wherever a door or window reaches the rail's height. A run longer than a rail needs a join, and an offcut is only worth keeping if it is long enough for another piece. So this calculator lays out each run and cuts every piece from as few rails as it can.
How the Plan Works
- Height decides which openings break the rail. A door with its architrave reaches the door height plus the reveal plus the architrave width. A window reaches from its sill to its head plus the same. If the rail is outside that band, it runs past.
- The rail stops at the architrave. Our reading, the same as skirting: no merchant guide covers it.
- No piece under 300mm, no join within 300mm of an opening. The same rules as our skirting calculator, and our own.
- Offcuts reused. Pieces are cut from rails longest first, so short pieces come out of offcuts.
What it does not do: rooms that are not rectangles, external corners, stairs, and panelling below the rail. For panelling, see our wall panelling calculator.
Rail Sizes, With Sources
Every rail in the dropdown has a Wickes product page, and no product page means no dropdown entry. All are 2400mm long.
| Rail | Product page |
|---|---|
| Dado, primed MDF 18 x 58mm, 2400mm | Wickes Dado Rail Primed MDF, 18 x 58 x 2400mm |
| Dado, pine 20 x 45mm, 2400mm | Wickes Pine Decorative Dado Rail, 20 x 45 x 2400mm |
| Picture rail, primed MDF 18 x 44mm, 2400mm | Wickes Primed MDF Picture Rail, 18 x 44 x 2400mm |
| Picture rail, primed MDF 18 x 44mm, 2400mm, pack of 4 | Wickes Primed MDF Picture Rail, 18 x 44 x 2400mm, pack of 4 |
Heights are from Skirting World's guides to dado rail height and picture rail height. Where the rail stops at an opening, and the joint rules, are our own.
Common Rooms: Rails Needed
Generated from the calculator above. Every room is 2400mm high with a 762mm door (1981mm high) and, where listed, a 1200mm window with its head at 2100mm. Dado rail at 960mm, picture rail at 2000mm, both 2400mm lengths. The last column is the usual sum.
| Room | Dado Rails | Picture Rails | Perimeter Less Doors, Over 2.4m |
|---|---|---|---|
| 3.0m x 2.5m, one door | 5 | 5 | 5 |
| 3.5m x 3.0m, one door | 6 | 6 | 6 |
| 4.0m x 3.5m, door and window | 6 | 6 | 6 |
| 4.0m x 3.5m, door, window sill 1000mm | 7 | 6 | 6 (short) |
| 5.0m x 4.0m, door and window | 7 | 7 | 8 |
| Hallway 4.5m x 1.2m, two doors | 5 | 5 | 5 |
Frequently Asked Questions
How much dado rail do I need?
The usual sum is the room's perimeter less the doors, divided by the rail length, and it can leave you short. For a 4.0m × 3.5m room with one door, and a window whose sill sits above the rail, it gives 6 rails of 2.4m, but the room needs 7. Rails cannot bend round corners, a join needs somewhere sensible to go, and an offcut is only useful if it is long enough for another piece. This calculator lays out every run between corners and openings, then cuts every piece from as few rails as it can.
How high should a dado rail be?
Skirting World's guide says there is no set rule, but gives wall height divided by 5 then doubled, which is 960mm on a 2400mm wall, and says anywhere between 900mm and 1000mm above the floor is safe. The calculator fills in that height from your wall height, and you can change it. We take the height as the top of the rail.
How high should a picture rail be?
Skirting World gives wall height minus 400mm, which is 2000mm on a 2400mm wall, and a range of 300 to 500mm below the ceiling. At that height a picture rail can hit the architrave over a standard door: a 1981mm door with a 5mm reveal and 69mm architrave reaches 2055mm. So in the default room the picture rail stops at the door. Raise it to 2100mm and it runs over the door instead, which changes the count from 6 rails to 7.
Does a window break the rail?
Only if the window and its architrave reach the rail's height. A dado rail at 960mm stops at a window with a 900mm sill, but runs straight under one with a 1000mm sill. That changes the default room from 6 rails to 7. Where the rail meets a door or window, the calculator stops it at the outside edge of the architrave, the same way skirting stops. No merchant guide covers this, so it is our reading.
Where do the joins go?
The calculator never cuts a piece shorter than 300mm and never puts a join within 300mm of a door or window. Those are the same rules as our skirting calculator, and they are our own, not a supplier's. The cutting plan lists every piece and which rail it comes from.
Should I buy a spare?
The answer is the cutting plan count, with nothing added, because the plan already reuses offcuts. A spare rail is shown on its own line if you want room for a mis-cut, which is easy to make on a mitre.