PlainwrenSquare footage calculator
Measure each room in feet and inches (or metres), add or take away parts such as a closet or a kitchen island, and get the total in square feet, square metres and square yards, plus how many boxes of flooring to buy.
How square footage is worked out
Area is length times width for a rectangle. The calculator does that for each row, adds the rows that share a room name, and takes away any row marked "Take away". Other shapes use their own formulas:
- Rectangle or square: length × width.
- Triangle: base × height ÷ 2 (the height is measured at a right angle to the base).
- Circle: π × diameter² ÷ 4. Half circle (a bay or a curved alcove): half of that.
- L-shaped or irregular rooms: split them into rectangles that do not overlap and enter each as a row with the same room name.
sq m = sq ft × 0.09290304 · sq yd = sq ft ÷ 9
The inches mistake
12 feet 6 inches is 12.5 feet, not 12.6, because a foot has 12 inches, not 10. Typing 12.6 when you mean 12' 6" overstates a 12' 6" × 10' room by 1 square foot, and the error grows with every wall. This calculator reads feet and inches as you would write them (12' 6", 12 ft 6 in, or just 12 6) and shows the decimal feet it used in the parts table, so you can check.
Worked example
An open-plan living area with a kitchen and a hallway, measured in feet and inches (the example filled in above):
- Living room: 15' 6" × 12' = 15.5 × 12 = 186 sq ft.
- Kitchen: 10' × 9' 6" = 10 × 9.5 = 95 sq ft, minus the island 6' × 3' = 18 sq ft (no flooring under it), so 77 sq ft.
- Hallway: 12' × 3' 6" = 12 × 3.5 = 42 sq ft.
- Total: 186 + 77 + 42 = 305 sq ft = 28.34 sq m = 33.89 sq yd.
- Flooring with 10% waste: 305 × 1.10 = 335.5 sq ft. Boxes cover 20 sq ft each, so 335.5 ÷ 20 = 16.8, rounded up to 17 boxes (340 sq ft). At 3.49 per sq ft, that is 340 × 3.49 = 1,186.60.
How much extra flooring to buy
Cuts at walls, doorways and around obstacles waste some material, and a few spare pieces are useful for repairs later. A common guide is about 5% extra for straight plank layouts in simple rooms, about 10% for most rooms, and 15% or more for diagonal or herringbone patterns and rooms with many corners. These are rules of thumb, not standards: the coverage printed on the box and your installer's advice for your layout come first. Boxes are always rounded up.
FAQ
How do I calculate square feet from feet and inches?
Turn the inches into a fraction of a foot by dividing by 12, then multiply length by width. 12' 6" × 10' 3" = 12.5 × 10.25 = 128.125 sq ft. The calculator does the conversion for you.
How do I measure an irregular or L-shaped room?
Split it into rectangles that do not overlap, measure each one, and enter each as its own row with the same room name. For a closet or bay, add a row; for something with no flooring under it, such as a kitchen island, add a row set to Take away.
How do I convert square feet to square metres?
Multiply by 0.09290304 (one foot is exactly 0.3048 m). 305 sq ft is 28.34 sq m. The calculator shows both, and square yards (sq ft ÷ 9), which carpet is sometimes sold in. For other conversions use the unit converter.
Should I measure to the wall or the baseboard?
Measure wall to wall at floor level. Flooring usually runs under the baseboard or leaves a small expansion gap hidden by it, and the waste allowance covers the difference.
Is my data saved?
No. The calculations run in your browser and nothing is stored. Use Print if you want to keep a copy of the results.