Room area calculator

How to use the room area calculator

This calculator returns floor area and perimeter for a rectangular or L-shaped room. For an irregular outline, split the floor into rectangles and add their areas, or use the floor planner to draw the outline.

1. Choose Feet / inches or Metres / cm.
2. Select the room Shape. Choose Rectangle or L-shape for the visible dimension fields.
3. Enter the Length and Width. Add any remaining amount in the plus inches fields.
4. For an L-shape, enter the Leg length (extends out) and Leg width (along the shared wall).
5. Read the floor area and perimeter in the selected unit system, with additional unit conversions shown below.

What to enter

Feet / inches

The default unit system. Enter major dimensions in feet and the plus inches fields in inches.

Metres / cm

Use metres for the major dimensions and centimetres in the plus inches fields.

Shape

Defaults to Rectangle. Choose L-shape to show the leg dimensions. A Polygon option may be available, but this page does not provide fields for entering its corner points.

Length

Main room length. Default: 12 ft in the default imperial setup, or 12 m when interpreted in metric.

plus inches

Additional amount for Length. Default: 0. Enter inches in imperial mode or centimetres in metric mode.

Width

Main room width. Default: 10 ft in the default imperial setup, or 10 m when interpreted in metric.

plus inches

Additional amount for Width. Default: 0. Enter inches in imperial mode or centimetres in metric mode.

Leg length (extends out)

L-shape leg distance extending from the main rectangle. Default: 6 ft in the default imperial setup. This field appears for an L-shape.

plus inches

Additional amount for the leg length. Default: 0. Enter inches in imperial mode or centimetres in metric mode.

Leg width (along the shared wall)

The L-shape leg span along the wall where it attaches. Default: 4 ft in the default imperial setup. It cannot exceed the main room width.

plus inches

Additional amount for the leg width. Default: 0. Enter inches in imperial mode or centimetres in metric mode.

Example: L-shaped room

Choose L-shape and use 12 ft Length, 10 ft Width, 6 ft Leg length (extends out), and 4 ft Leg width (along the shared wall). Leave all four plus inches fields at 0. Main rectangle: 12 × 10 = 120 sq ft. Leg: 6 × 4 = 24 sq ft. Floor area: 120 + 24 = 144 sq ft, which is 16 sq yd and 13.38 m² after rounding. Main rectangle perimeter: 2 × (12 + 10) = 44 ft. Extra perimeter from the leg: 2 × 6 = 12 ft. Total perimeter: 44 + 12 = 56 ft, which is 17.07 m.

How the room area calculation works

For imperial entries, each dimension equals the major feet value plus the minor inches value divided by 12. For metric entries, the major value is in metres and the minor value is in centimetres. For a rectangle, area = length × width and perimeter = 2 × (length + width). For an L-shape, the calculator adds leg length × leg width to the main rectangle area. It adds 2 × leg length to the main rectangle perimeter because the leg attaches flush to one wall. Results are rounded to two decimal places.

Reading the results

The summary uses your selected unit system: sq ft and ft for Feet / inches, or m² and m for Metres / cm. The detailed results also show area in sq ft, m², and sq yd, plus perimeter in ft and m. Perimeter can help estimate baseboard, trim, or edging.

Limitations and common mistakes

• The visible form does not provide corner-point fields for an irregular polygon. For an irregular room, split the floor into rectangles and add their areas, or use the floor planner to draw the outline.
• An L-shape assumes the leg attaches flush to one wall of the main rectangle. Its leg width cannot be greater than the main room width.
• The calculator reports measured area only. It does not add a flooring waste allowance.
• Measure wall to wall at floor level. Minor dimensions must be zero or positive, and the main and leg dimensions must be positive.

Frequently asked questions