400 square feet is the area of a 20 × 20-foot square. It is also 37.16 square meters (approximately). The number describes floor area; it does not tell you the shape or how much usable space remains after walls, closets, fixtures, or other features.
| Example shape | Dimensions | Area |
|---|---|---|
| Square | 20 × 20 ft | 400 sq ft |
| Rectangle | 16 × 25 ft | 400 sq ft |
| Rectangle | 10 × 40 ft | 400 sq ft |
Each example has the same area but a different shape and proportion.
A square room measuring 20 feet on each side contains 400 square feet, because 20 × 20 = 400.
20 feet
+----------------------+
| |
20 feet | 400 sq ft |
| |
+----------------------+
Dimension diagram only; it is not a floor plan or a scale drawing.
Before comparing furniture or planning a layout, measure the clear interior and mark doors, closets, windows, and fixed features. A room's total area alone does not establish that a particular layout will fit.
For a rectangle, multiply length by width. To find one side when the other is known, divide 400 by that measurement.
A 20 × 20-foot outline is not the only way to use 400 square feet. Narrower and longer shapes can have the same area while creating a very different room.
Using NIST's exact international-foot conversion, 400 sq ft = 37.161216 m², usually rounded to 37.16 m².
Yes, if both clear interior dimensions are 20 feet: 20 × 20 = 400 square feet.
The stated area is 400 square feet. The actual measured floor area depends on which boundaries are included in the measurement.
Area alone cannot establish whether a room feels large or works for a particular use. Shape, ceiling height, openings, furniture, and the activities planned all affect that judgment.
For a smaller example, see how big 300 square feet is.