Square footage calculator

For a rectangle, square footage is just length × width: a 12 × 14 ft bedroom is 168 sq ft. Real rooms have bump-outs, closets, chimney chases and angled walls. This calculator handles them two ways.

Walk the walls. Start in a corner and enter each wall as a direction and a length: right, down, left, up, or any angle. The floor plan is drawn as you go. If the last wall does not end where you started, the calculator adds the closing wall and shows its length. If two walls cross, usually from a typo in a direction, you get a warning.

Stack rectangles. Add rectangles for each part of the room and subtract the ones you will not cover, such as a kitchen island or a fireplace hearth.

You get:

• floor area in square feet (and square meters)
• perimeter, for baseboard and trim
• wall area at your ceiling height
• room volume in cubic feet, handy for heating and cooling
• a material and cost line from your price per square foot

Everything runs in your browser with no sign-up, and you can export the numbers and the drawing to PDF or Excel for free.

From each wall's direction and length, the calculator finds the corner coordinates and then uses the shoelace formula for the area of a polygon:

Area = ½ × |Σ (xᵢ × yᵢ₊₁ − xᵢ₊₁ × yᵢ)|

In words: cross-multiply the coordinates of each wall's start and end points, add up the differences, and halve the result. It works for any shape whose walls do not cross: L, T and U shapes, bump-outs and angled corners. Perimeter is the sum of the wall lengths, including the closing wall.

Wall area is perimeter × ceiling height. Room volume is floor area × ceiling height. Doors and windows are subtracted in the paint calculator when you get to painting.

Example: start at the top-left corner. Walk right 20 ft, down 14 ft, left 8 ft, up 6 ft, left 12 ft. You are now 8 ft below the start, so the calculator adds an 8 ft closing wall.

Corners: (0, 0), (20, 0), (20, 14), (12, 14), (12, 8), (0, 8).

1. Area: 20 × 8 + 8 × 6 = 208 sq ft (the shoelace formula gives the same)
2. Perimeter: 20 + 14 + 8 + 6 + 12 + 8 = 68 ft
3. Wall area with 8 ft ceilings: 68 × 8 = 544 sq ft
4. Volume: 208 × 8 = 1,664 cu ft
5. Cost: flooring at $3.50 per sq ft (enter your own price) = 208 × 3.50 = $728

In metric, the same steps work in meters: right 6, down 4, left 2, up 2, left 4, plus a 2 m closing wall, is 16 m² with a 20 m perimeter.

Angled wall: a 15 × 15 ft room with one corner cut at 45 degrees. Walk right 15, down 9, down-left at 45 degrees for 8.49 ft, left 9, and close 15 ft. Area: 225 − 18 = 207 sq ft; perimeter 56.5 ft.

If it is easier, build the room from rectangles:

• Living area: 12 × 14 = 168 sq ft
• Dining nook: 6 × 8 = + 48 sq ft
• Kitchen island: 3 × 2 = − 6 sq ft
• Total: 210 sq ft

Keep rectangles from overlapping, or the shared part is counted twice. Then add a waste allowance for flooring in the laminate flooring calculator or the tile calculator, which round to boxes and pieces.

Carpet is often priced per square yard: 208 sq ft ÷ 9 = 23.1 sq yd.

• Go around in one direction. Turning back halfway makes walls cross; the calculator flags it.
• Let the calculator close the shape. If you also measure the last wall, compare it with the closing length. A big gap means a measuring error somewhere.
• Measure at floor level and round up to the nearest inch.
• Convert inches correctly. 10 ft 6 in is 10.5 ft, not 10.6.
• Room totals are not listed home size. Official square footage for a home sale is measured by different rules; room totals are for materials.
• Measure angled walls along the wall. For a clipped corner, measure the two legs and let the angle and length follow.