What the Room Perimeter Calculator actually calculates
Gross perimeter is twice length plus twice width. The trim result subtracts the entered opening widths and cannot fall below zero. This is installed run length, not an order optimized for stock lengths, corner cuts, returns, or offcuts; no purchase allowance is added automatically.
The calculation path
A rectangular perimeter equals twice the sum of room length and width.
Inputs that can change the answer
- Length: Enter length in m.
- Width: Enter width in m.
- Door widths to exclude: Enter door widths to exclude in m.
Checks that stay outside the formula
Add 5–10% when buying patterned or joint-sensitive trim.
A practical order for entering the data
- Measure the internal length and width of the rectangular room.
- Add the widths of doorways where the intended trim will stop.
- Use gross perimeter for uninterrupted runs or the reduced trim length for runs excluding those doorways.
Engine check using the prefilled sample
Worked example: length = 4 m, width = 3.5 m and door widths to exclude = 0.9 m. Replace the sample dimensions with measurements from the room; split irregular areas into simpler sections where needed.
Results for these inputs
- Gross perimeter
- 15.00 m
- Trim length
- 14.10 m