How to Measure Square Footage of a Room, Yard or Irregular Space

Almost every material estimate starts with the same number: how many square feet you have. Flooring, paint, sod and tile are all priced and packed by area, so a measuring mistake here follows you through the whole shopping list. The method below works for a bedroom, a deck or a lawn, and it needs nothing more than a tape measure.

What you need

• A tape measure. A 25 ft tape is enough for most rooms; for a yard, a long tape or a measuring wheel is faster.
• Paper and a pencil, to sketch the space and write every number down as you measure it.
• A second person to hold the end of the tape on long distances, if you can.

Step by step

1. Sketch the space. Draw its outline roughly. It does not need to be to scale, but mark every corner.
2. Split the sketch into simple shapes. Start with rectangles and use triangles or circles only where you must. An L-shaped room is two rectangles.
3. Measure every side in the same unit. Pick feet (with decimals) or inches and keep it. Measure wall to wall at floor level and write each number on the sketch right away.
4. Calculate each shape. Rectangle: length × width. Triangle: ½ × base × height. Circle: π × (diameter ÷ 2)².
5. Add what you will cover and subtract what you will not, such as a kitchen island, a tub or a patio.
6. Add an allowance for waste if you are buying material. How much depends on the material (see the table below).

Worked example: an L-shaped room

Rectangle A is 14 × 10 ft = 140 sq ft. Rectangle B is 6 × 4 ft = 24 sq ft. The room is 140 + 24 = 164 sq ft.

If a 3 × 2 ft closet inside rectangle A will not get the new floor, subtract it: 164 − 6 = 158 sq ft of floor to cover. The Square Footage Calculator does each rectangle, triangle or circle for you.

Worked example: a lawn with a round flower bed

The lawn is 40 × 25 ft = 1,000 sq ft. A round bed 6 ft across takes π × 3² = 28.27 sq ft out of it, so the area to cover is 1,000 − 28.27 = 971.73 sq ft.

With about 5 % extra for cuts you would buy 1,020.31 sq ft of sod. In 10 sq ft rolls that is 103 rolls, or 3 pallets at 450 sq ft each. In the Sod Calculator, type the bed into "Area without sod".

Feet and inches

Calculators want one unit. To turn inches into a fraction of a foot, divide by 12 and add the whole feet: 10 ft 6 in is 10.5 ft. The common ones:

Keep the decimals while you calculate and round only the final answer.

How much extra to add

The area you measured is the area you cover. What you buy is a little more, because cutting around edges wastes material.

Rooms with many corners, diagonal layouts or curves usually waste more. The extra is an allowance you choose, not a rule.

Measuring walls for paint

For paint you need wall area, not floor area: perimeter × wall height, minus the openings. A 14 × 12 ft room has a perimeter of 2 × (14 + 12) = 52 ft. With 8 ft walls that is 52 × 8 = 416 sq ft. The Paint Calculator counts a standard door as 21 sq ft (3 × 7 ft) and a window as 15 sq ft (3 × 5 ft), so one door and two windows remove 51 sq ft and leave 365 sq ft of wall for one coat.

Common mistakes

• Mixing units. Multiplying feet by inches gives a number that means nothing. Convert first.
• Rounding too early. Round each side to a whole number and a big room can be off by a few square feet.
• Forgetting the small spaces. Alcoves, bay windows and the space under a door all count if you will cover them.
• Counting an overlap twice. Where two rectangles meet, split the room along one line, as in the diagram.
• Measuring a different way on each wall. Decide whether you measure to the baseboard or to the wall surface and do it everywhere.