Measurement basis
Not every room can be measured as one simple rectangle. This calculator supports a rectangular room, an L-shaped room made by removing a corner rectangle, and a circular floor. It reports net area and an appropriate outline perimeter so you can begin a flooring or trim takeoff. The L-shaped mode assumes the cutout touches two adjacent outer sides, not a hole inside the room. Work from a sketch and label every measurement before entering it. Alcoves, bay windows, curved edges, and irregular polygons should be split into simpler shapes and reconciled separately.
Geometry, units and worked example
A worked example
A 16 × 12 ft rectangle has 192 sq ft and a 56 ft perimeter. Removing a 6 × 4 ft corner gives 168 sq ft while keeping a 56 ft outline perimeter.
Enter consistent dimensions
- Sketch the room and select the matching geometric shape.
- Measure to the finished boundaries and record cutout dimensions if needed.
- Use net area for coverage and the perimeter as a starting point for trim.
Where the model stops
- Perimeter is the geometric outline before deducting door openings or adding returns for baseboard.
- Carpet roll width and plank layout can require more material than net area suggests.
- For a circle, the length input is the diameter, not the radius; the width and cutout inputs are ignored.
Frequently asked questions
How do I calculate square footage of an L-shaped room?
Calculate the full outside rectangle and subtract the rectangular corner that is missing.
Why does the L-shaped perimeter match the outer rectangle?
Removing a rectangular outside corner replaces two removed lengths with two equal new inside lengths.
Is floor area the same as the quantity of carpet I need?
Not always. Roll width, seams, direction, and offcuts can increase the purchased carpet above net floor area.
Calculation method: JICWH methodology. Examples are planning assumptions, not product recommendations.