Interior Trim Length Calculator

Interior Trim Length Calculator

Interior trim doesn't run across doorway openings - this calculator subtracts doorway widths from the room perimeter to give a more accurate material estimate than a simple perimeter figure alone.

Formula

Net Trim Length = Room Perimeter - (Doorways x Average Doorway Width)
Trim to Purchase = Net Trim Length x 1.1 waste factor

Example

A 48 ft room perimeter with 2 doorways averaging 3 ft wide:

Net Trim = 48 - 6 = 42 ft → Trim to Purchase = 46.2 ft

Why the Waste Factor Matters Here

The 10% waste factor accounts for angled miter cuts at inside and outside corners, which consume more material than a straight butt cut would - trim with many corners (an irregularly shaped room, or one with alcoves and bump-outs) burns through material faster than this baseline estimate suggests, so consider bumping the waste allowance higher for complex room shapes.