How to Measure the Square Footage of a Room

Almost every home project starts with one number: the area you are covering. Flooring, tile, paint, drywall and even mulch are all priced and packed by area or volume, so a good measurement saves you money and a second trip to the store. Here is how to measure any room, including awkward shapes.

Last updated 2026-11-12

What you need

• A 25 ft tape measure (or a laser measure for large rooms)
• A pencil and paper, or your phone's notes app
• A rough sketch of the room, not to scale, so you can label each measurement

Step 1: Measure a rectangular room

Measure the length of the room from wall to wall at floor level, then the width. Write both down in feet and inches. Multiply them:

Example: a room 12 ft 6 in long and 10 ft wide. First turn the inches into a decimal: 6 in ÷ 12 = 0.5, so 12.5 ft. Then 12.5 × 10 = 125 sq ft.

Walls are rarely perfectly straight. Measure each dimension in two places, such as near each end of the room, and use the larger number.

Step 2: Split L-shaped and irregular rooms into rectangles

For an L-shaped living room, draw a line that divides the L into two rectangles. Measure each one and add the areas. For example, a 20 × 12 ft main area plus a 8 × 6 ft dining nook is 240 + 48 = 288 sq ft. Any room, however odd, can be broken into rectangles, plus occasionally a triangle or a half circle.

Our flooring calculator lets you add each rectangle as a separate "room" and sums them for you.

Step 3: Triangles, circles and bay windows

Step 4: Measuring walls instead of floors

For paint, wallpaper and drywall you need wall area, not floor area. Add up the length of every wall (the perimeter) and multiply by the ceiling height. A 12 × 14 ft room with 8 ft ceilings has a perimeter of 52 ft and a wall area of 52 × 8 = 416 sq ft.

Subtract large openings if you want a tighter estimate: a standard interior door is about 20 sq ft and an average window about 15 sq ft. The paint calculator and drywall calculator do this automatically.

Step 5: Measuring depth for volume

Concrete, gravel, mulch and soil are sold by volume, so you also need a depth. Measure depth in inches and divide by 12 to get feet, then multiply by the area. Divide cubic feet by 27 to get cubic yards.

See the concrete, gravel and mulch calculators for this step.

Worked example: measuring a whole floor for one order

Suppose you are putting new vinyl plank through a living room, a hallway and a closet. Sketch the plan, then measure and write each rectangle down:

With an 8% waste allowance for a straight layout that is 314.6 sq ft; in boxes of 23.6 sq ft you would buy 14 boxes (330.4 sq ft). Laying it diagonally instead? Read flooring waste for diagonal layouts before choosing the percentage. You can enter all three areas as separate rooms in the flooring calculator.

Measuring gable walls and sloped ceilings

Rooms with vaulted ceilings or attic rooms have walls that are not simple rectangles. A gable wall is a rectangle with a triangle on top. Measure the width of the wall, the height up to where the slope begins, and the extra height to the peak:

Example: a 14 ft wide wall that is 8 ft tall at the sides and 12 ft at the peak is 14 × 8 = 112 sq ft plus 14 × 4 ÷ 2 = 28 sq ft, for 140 sq ft. For a sloped ceiling, measure along the slope (not the floor below it) for the length, because the surface you paint or drywall is longer than the floor it covers.

Measuring stairs

Flooring and carpet on stairs are measured per step rather than by area. For each step, measure the tread depth (the part you stand on, including the nosing) and the riser height, then multiply their sum by the stair width. A straight staircase of 13 steps, each with a 10.5 in tread and a 7.5 in riser and a width of 36 in, needs (10.5 + 7.5) × 36 ÷ 144 = 4.5 sq ft per step, or about 58.5 sq ft in total. Many stair products, such as stair nosings and tread kits, are sold per step, so count the steps as well as the area.

Common measuring mistakes

• Mixing inches and feet. 10 ft 3 in is 10.25 ft, not 10.3 ft. Always convert inches by dividing by 12.
• Forgetting closets and hallways when the floor continues into them.
• Measuring at the baseboard. For flooring, measure wall to wall; the baseboard comes off or sits over the expansion gap.
• Skipping the waste allowance. The measured area is what you cover; you always buy a little more. Read how much waste to add.

Metric conversions

Which measurement each project needs