Picture Rail Calculator

This calculator determines the total length of picture rail moulding needed for your room, the number of standard lengths to purchase, mitre joint count, adhesive and pin nails.

Rail length

Total rail = Room perimeter − Door openings. Where the rail stops at a door it is interrupted by the whole lining-and-architrave assembly, not just the 762mm leaf — a standard UK doorset (1981 × 762mm leaf, ~32mm lining and ~69mm architrave each side) blocks roughly 0.95m of wall, so each obstructing door is deducted at 0.95m.

This deduction only applies when the rail meets the architrave head. A standard architrave head tops out around 2050mm, so if you set the rail to 2100mm it runs continuously above the doors and no door deduction is made.

Lengths to buy

Lengths = ceil(Total rail / Standard length). Picture rail typically comes in 2.4m or 3.0m lengths from UK timber merchants. Buy one or two extra lengths to allow for mitre waste and any mistakes.

Mitre joints

Each corner requires a mitre joint. Internal corners can be coped for a better fit on walls that aren't perfectly square. External corners (chimney breasts, bay windows) must be mitred at 45 degrees.

Fixings

• Grab adhesive: ~1 tube per 8m of rail
• Pin nails: a generous estimate of ~1 per 600mm. Panel pins only hold the rail while the grab adhesive cures, so UK fitting guides pin near each corner then at roughly 600mm–1m intervals — round up and you will have plenty

Standard heights

Picture rail is installed between 1.8m and 2.1m from the floor, typically 300-500mm below the ceiling. In a standard 2.4m ceiling room, 2.0m from the floor is most common.