Floor area in square metres and square feet, wall area, perimeter and volume for one or more rectangular rooms or an L-shaped room.
By AdminDrafted with AI writing toolsUpdated Checked examples: 4
The floor covers 19 m² (204.5 ft²). With a 2.7 m (8.86 ft) ceiling the walls add up to 64.8 m² (697.5 ft²) before doors and windows, and the room holds 51.3 m³ (1,812 ft³) of air.
Each rectangle is treated as its own room with four walls. If the rectangles are parts of one open room, the shared edges are not real walls and the wall area is an overestimate.
Floor area is length × width for each rectangle, summed; an L-shaped room is its enclosing rectangle minus the missing corner. Wall area is the perimeter times the ceiling height, before doors and windows are taken off, and volume is floor area times ceiling height. Every result is given in metric and imperial units, using the exact foot of 0.3048 m, so 1 m² = 10.764 ft².
People use it to order flooring, paint or plasterboard and to size heating or ventilation by room volume. The default, a 4 × 3.5 m room plus a 2.5 × 2 m alcove under a 2.7 m ceiling, gives 19 m² (204.51 ft²) of floor, 64.8 m² of wall and 51.3 m³ of air.
Each rectangle is counted as a separate room with four walls. When the rectangles are parts of one open space, the wall area comes out too high; use the L-shape option for that case.
Multiply the room's length by its width, both in feet: a 12 × 10 ft room is 120 ft². Measure at floor level from finished wall to finished wall, and convert inches first, since 4 in is 0.3333 ft, not 0.4 ft. Split an irregular room into rectangles and add them.
With measurements in inches, multiply the inches and divide by 144, because a square foot is 12 × 12 in.
A bedroom measuring 13 ft 4 in by 11 ft 9 in, with a closet 5 ft 6 in by 2 ft 2 in:
Reading 13 ft 4 in as 13.4 ft and 11 ft 9 in as 11.9 ft gives 159.46 ft² for the bedroom alone, 2.79 ft² too much, because inches are twelfths of a foot, not tenths.
With straight walls at right angles, draw the outline and cut it into rectangles that do not overlap. Alcoves, closets and hallway strips each become one.
For angled walls and bay windows, a triangle is ½ × base × height and a trapezoid is the average of its parallel sides times the depth: a bay 6 ft wide at the wall, 4 ft across the front and 2 ft deep covers (6 + 4) ÷ 2 × 2 = 10 ft².
For curved or many-sided outlines, the area and perimeter calculator covers 15 shapes including circles and ellipses. The polygon area calculator takes the corner points of any straight-sided outline.
An L-shaped room can be measured two ways, and both give the same floor area. Take a living room whose outline is 20 × 16 ft with an 8 × 6 ft corner missing:
The walls differ. The L's perimeter equals its enclosing rectangle's, 2 × (20 + 16) = 72 ft, so an 8 ft ceiling gives 576 ft² of wall.
Treating the two rectangles as separate rooms gives 736 ft², because the 10 ft edge they share is counted as a wall on both sides: 2 × 10 × 8 = 160 ft² of wall that does not exist.
The international foot is exactly 0.3048 m; the older US survey foot was retired at the end of 2022 (NIST). Squaring the foot gives exact factors: 1 ft² = 0.09290304 m², and 1 m² = 10.7639 ft². A square yard is 9 ft², or 0.83612736 m².
| Room (ft) | Square feet | Square meters | Square yards |
|---|---|---|---|
| 10 × 10 | 100 | 9.29 | 11.11 |
| 10 × 12 | 120 | 11.15 | 13.33 |
| 12 × 12 | 144 | 13.38 | 16.00 |
| 12 × 14 | 168 | 15.61 | 18.67 |
| 12 × 16 | 192 | 17.84 | 21.33 |
| 14 × 16 | 224 | 20.81 | 24.89 |
| 15 × 20 | 300 | 27.87 | 33.33 |
| 20 × 20 | 400 | 37.16 | 44.44 |
The slip to avoid is using the length factor for an area. A meter is 3.28 ft, but a square meter is 3.28 × 3.28 = 10.76 ft². Dividing the 168.58 ft² bedroom by 3.28 gives 51.40, more than three times its real 15.66 m².
For single conversions, use the square feet to square meters converter.
Flooring is sold in whole cartons, and cutting to fit walls, doorways and row ends wastes some of it. Use the allowance in the installation instructions for the product you are buying.
Bruce's solid hardwood instructions, for example, add 5% to the measured area for cutting and grading, 10% for diagonal installations and 10–15% for glue-down installations. For the 168.58 ft² bedroom and a carton that covers 20 ft²:
Round up once, at the end. Rounding each dimension up first already adds area: taking the bedroom as 13 ft 6 in × 12 ft gives 162 ft² against the real 156.67 ft², 3.4% extra before any allowance.
Include closets and door openings the flooring runs into, and leave out areas it will not cover, such as the floor under fixed kitchen cabinets. The tile calculator does the same carton arithmetic for tiles, including grout joints.
160 x 141 and 66 x 26 for the bedroom and closet in inches. All lines share one unit: m, cm, ft or in.5 x 2 for the 10 ft² bay; its walls will not match the real ones.For paint, the paint calculator works from the real walls and takes off doors and windows.
A house's official square footage is not the sum of its rooms. ANSI Z765-2021, the US standard for single-family houses, measures finished area at floor level to the outside finished surface of the exterior walls.
It leaves out garages, counts finished space only where the ceiling is at least 7 ft high (with exceptions under beams and for sloped ceilings), reports below-grade area separately and rounds to the nearest square foot.
Measured to the outside walls and including hallways and stairs, a house's figure comes out larger than its rooms added together.
Checked against: 4×3.5 + 2.5×2 = 19 m²; perimeters 15 + 9 = 24 m; ÷ 0.3048² for ft²
Checked against: Hand calculation: 12 × 10 = 120 ft²; 2(12 + 10) × 8 = 352 ft²; 120 × 8 = 960 ft³
Checked against: Hand calculation: 30 − 6 = 24 m²; an L-shape's perimeter equals its bounding rectangle's, 2(6 + 5) = 22 m
Checked against: 3 m × 3 m square, 2.5 m ceiling
Multiply the length by the width, both in feet. A 12 × 10 ft room is 120 ft². For an irregular room, split the floor into rectangles, work out each one and add them: a 12 × 10 ft room with a 4 × 3 ft closet totals 132 ft². Measurements in inches divide by 144 to give square feet.
Take the rectangle that encloses the room and subtract the missing corner. A 6 × 5 m room with a 2 × 3 m cut-out is 30 − 6 = 24 m². The perimeter equals the enclosing rectangle's, 2 × (6 + 5) = 22 m, so under a 2.4 m ceiling the walls total 52.8 m².
10.7639. The foot is exactly 0.3048 m, the only definition NIST uses since the US survey foot was retired on 1 January 2023 (NIST Handbook 44, Appendix C), so 1 m² = 1 ÷ 0.3048² ≈ 10.764 ft² and 1 ft² ≈ 0.0929 m². A 19 m² room is 204.51 ft², and a 120 ft² room is 11.15 m².
In US homes, 7 ft for habitable rooms and 6 ft 8 in for bathrooms, toilet rooms and laundry rooms (2021 IRC R305.1; 2024 IRC R313.1). A 12 × 10 ft room at the 7 ft minimum holds 840 ft³ of air, against 960 ft³ at 8 ft. The section's exceptions and local amendments can change the figure.
Multiply the perimeter by the ceiling height, then subtract doors and windows. A 12 × 10 ft room with an 8 ft ceiling has 2 × (12 + 10) × 8 = 352 ft² of wall. This calculator reports the gross figure; the paint and drywall calculators take off openings.
This calculator includes 4 worked examples with independently sourced answers. They run in the test suite, and you can run them here too.