Square Footage Calculator

How to calculate square footage?

Measure length and width in feet, then multiply: Length × Width = Square feet. This works the same whether you're measuring a room, a roof footprint, a tile installation, or a countertop — anywhere the base shape is (or can be split into) a rectangle.

Use a tape measure or laser measure and take each dimension wall to wall at floor level, along the longest straight run. Round to the nearest inch and convert inches to decimal feet before multiplying: 6 inches is 0.5 ft, 3 inches is 0.25 ft, so 12 ft 6 in becomes 12.5 ft. Multiplying feet-and-inches as if they were decimals (treating 12'6" as 12.6) is the most common source of small errors. Measure twice in older houses, where walls are rarely perfectly parallel; if the two readings for the same wall differ, use the larger one so you don't come up short on material.

Formula & methodology

Each section's area depends on its shape. A rectangle is Length × Width. A triangle is ½ × Base × Height, where the height is measured at a right angle to the base, not along the sloping side. A circle is π × (Diameter ÷ 2)², so you only need one measurement straight across the middle. Sections entered in meters are converted to square feet (1 m² ≈ 10.7639 sq ft) before they are added, so mixed rooms stay comparable in the breakdown.

The total is the sum of every section's area. From that total, square yards = total ÷ 9, square meters = total ÷ 10.7639, and acres = total ÷ 43,560 — the standard conversion factors for each unit. Open "Show the math" under the results to see every section's formula with your own numbers plugged in, the running sum and each conversion.

Square footage of an irregular room

Split an L-shaped, T-shaped, or otherwise irregular room into simple shapes, measure each one separately, and use "Add section" for each — the calculator sums every section's area automatically. Give each section a label (like "Main area" and "Alcove") to keep the breakdown easy to read. Sketch the floor plan on paper first and write each dimension on the drawing; it makes missed or double-counted areas obvious.

• L-shaped rooms: draw a line from the inside corner straight to the opposite wall. You now have two rectangles that don't overlap — enter each as a rectangle section.
• Angled walls and corners: a wall cut across a corner leaves a right triangle. Measure the two straight walls it connects (base and height) and enter a triangle; if the corner is missing from an otherwise square room, subtract it instead by measuring the room without that corner.
• Bay windows: an angled bay is usually a rectangle in the middle with a triangle on each side. A half-round bay is half of a circle — enter the circle with the bay's full width as the diameter, then halve that section's area (a 6 ft wide half-round bay adds about 14.14 sq ft).
• Round rooms and features: measure the diameter through the center at its widest point and use a circle section.
• Closets and alcoves: measure them as separate rectangles. Include them when buying flooring that runs into them; leave them out if you only want the open floor area of the room.

Once you have the floor area, the flooring calculator turns it into boxes with a waste allowance, and the tile calculator adds tile count, mortar and grout for kitchens and bathrooms.

Worked example: an L-shaped living room

Picture a living room whose main area is 18 ft long and 14 ft wide, with a reading nook off one end that is 8 ft wide and 6 ft deep. Split it at the inside corner into two rectangles:

• Main area: 18 ft × 14 ft = 252 sq ft
• Nook: 8 ft × 6 ft = 48 sq ft
• Total: 252 + 48 = 300 sq ft

That is 300 ÷ 9 ≈ 33.33 square yards, 300 ÷ 10.7639 ≈ 27.87 square meters, and about 0.0069 acres. To check it, measure the whole outline instead: the outer rectangle is 18 × 20 ft = 360 sq ft, and the empty corner beside the nook is 10 × 6 ft = 60 sq ft, so 360 − 60 = 300 sq ft. When the add-up and the subtract method agree, you can trust the measurements. Entering the two rectangles above (in meters, 5.49 × 4.27 m and 2.44 × 1.83 m) gives the same total within rounding.

Square feet, square yards, square meters and acres

Carpet is often priced per square yard, flooring and paint coverage per square foot, and plans outside the US in square meters. The table converts common areas; for any other value, use the square feet to square meters converter.

Factors: 1 sq yd = 9 sq ft; 1 m² = 10.7639 sq ft (1 ft = 0.3048 m exactly); 1 acre = 43,560 sq ft. Values rounded to two decimals (acres to four).

How big is 1,000 sq ft?

A thousand square feet is about 92.9 m² or 111 square yards. As a square, it would measure about 31.6 × 31.6 ft; as a rectangle, it could be 40 × 25 ft or 50 × 20 ft. That same area could hold almost seven 12 × 12 ft rooms (144 sq ft each), with a little left over for a hallway. Areas like this are easier to picture by pacing them out: an average adult stride is roughly two and a half feet, so about a dozen paces covers 31.6 ft.

Wall area is a different number from floor area. If you're painting, the paint calculator works from wall height and room perimeter, so a 1,000 sq ft floor plan can mean well over 2,000 sq ft of wall surface once every room is counted.

How home square footage is measured

The square footage on a US listing or appraisal is not simply the sum of every room. Most appraisals follow ANSI Z765-2021, the American National Standard for measuring single-family homes, which Fannie Mae has required for appraisals since April 1, 2022. Its main rules:

• Measure to the exterior finished surfaces of the outside walls, so wall thickness is included, and report the result to the nearest whole square foot.
• Only finished area counts toward gross living area. Garages, unfinished basements and unfinished attics are excluded.
• Finished space needs a ceiling height of at least 7 ft. Under a sloped ceiling, at least half the room must reach 7 ft, and any part lower than 5 ft is not counted.
• Any level that is partly or fully below grade is reported separately from above-grade living area, even when it is finished to the same standard.

Because of these rules, an interior room-by-room measurement like the one this calculator does will usually come out smaller than the official figure, which includes walls. Listings can differ again: some agents use the county tax record, the builder's plan or a figure that includes a finished basement, so two numbers for the same house are common. For a purchase or appraisal dispute, ask which method each figure used. For flooring, paint and furniture planning, interior measurements are the ones you want.

Splitting rent by square footage

Add each roommate’s room as its own section with a name, enter the total rent in the optional field above, and the Sections breakdown shows each room’s percentage of the total floor area and its proportional share of the rent — a common, straightforward way to split rent fairly when bedrooms differ in size.

Each share is the room's area divided by the total, multiplied by the rent. Two bedrooms of 180 and 120 sq ft with $1,500 rent split 60/40: $900 and $600. Many households first split shared space (kitchen, living room, bathroom) equally and apply the area split only to the private rooms; to do that, enter just the bedrooms here with the portion of rent you've assigned to private space, then add the equal shares on top.