Door Frames – Jamb Widths & Trim Sets

Instead of working from a supplier's ballpark figure, this calculator derives your door frames requirement from Jamb Depth = Wall Thickness; Casing Length = 2 × H + W + 10 cm per frame using the exact door size and wall thickness you provide. The arithmetic stays transparent: each result links back to the displayed formula, so you can audit any number. For instance: A 0.9 × 2.1 m door in a 125 mm wall: jambs at 125 mm, casing run 2 × 2.1 + 0.9 + 0.1 = 5.2 m per side. Keep in mind: Round door frames up to the next whole purchasable unit. Quantities are rounded conservatively so offcuts, spillage and delivery shortages never stop work mid-job.

1. 1

   Measure the space

   Record the door size and wall thickness at the widest and longest points.

2. 2

   Enter the values

   Type the measurements into the calculator and select your units.

3. 3

   Apply the formula

   The tool computes Jamb Depth = Wall Thickness; Casing Length = 2 × H + W + 10 cm per frame for your inputs instantly.

4. 4

   Add waste and order

   Review the total with a 5-10% margin and round up to whole units.

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