Rectangle Square Feet Calculator

Updated 12 November 2026 · Standard formula, shown below

Area 120.00 sq ft

Length: 12 ft; You entered
Width: 10 ft; You entered

This calculator works out the area of a rectangle in square feet when you enter its length and width. Type in the two dimensions in feet (or inches, which it converts automatically), and you get the total square footage instantly. It is the quickest way to find floor area for tiling, carpeting, painting, or any other rectangular space.

Formula

The formula is simple:

Area (sq ft) = Length (ft) × Width (ft)

Where:

Length – the longer side of the rectangle, measured in feet.
Width – the shorter side, also in feet.
Area – the result, in square feet (sq ft or ft²).

If you measure in inches, first convert to feet by dividing by 12 (since 1 ft = 12 in). For example, 6 inches = 0.5 ft.

Worked Example

Using the default values (Length = 12 ft, Width = 10 ft):

Area = 12 ft × 10 ft
Area = 120 sq ft

The calculator shows 120.00 sq ft. That matches the formula exactly.

When to Use This Calculator

Use it for any flat rectangular surface:

Room floor area for flooring, carpet, or tile.
Wall area for paint or wallpaper.
Garden or lawn area for sod or fertilizer.
Countertop or table surface area.
Driveway or patio area for concrete or pavers.

It works for any rectangle, whether it’s a small closet or a large warehouse.

How to Read the Result

The result is the total area in square feet. For example, 120 sq ft means you need enough material to cover 120 square feet. If you’re buying flooring, add about 10% extra for waste and cuts. For paint, divide the area by the coverage per gallon (usually around 350–400 sq ft per gallon) to get the number of gallons needed.

Remember that square feet measure area, not length. A 10×12 room is 120 sq ft, but a 20×6 room is also 120 sq ft – the shape matters for layout, but the area is the same.

Common Mistakes and Unit Mix-Ups

Mixing feet and inches: If you measure one side in feet and the other in inches, you’ll get a wrong answer. Convert everything to the same unit first.
Forgetting to convert inches to feet: 12 inches is 1 foot, so 6 inches = 0.5 ft. Many people mistakenly use 6 as if it were feet.
Using the wrong formula: For a triangle, you divide by 2; for a circle, you use πr². This calculator is only for rectangles.
Rounding too early: If you convert 1 ft 8 in to 1.67 ft, that’s fine, but don’t round to 1.7 ft unless you’re okay with a small error.

Limitations of the Formula

The formula assumes a perfect rectangle – four right angles and opposite sides equal. Real rooms often have alcoves, bay windows, or irregular shapes. In those cases, break the space into rectangles, calculate each area, and add them together. For very irregular shapes, consider a more advanced method or professional measurement.

Also, the calculator gives the area in square feet. If you need square yards (common for carpet), divide by 9 (since 1 sq yd = 9 sq ft). For square meters, multiply by 0.0929.

Frequently Asked Questions

How do I convert inches to feet for this calculator?
Divide the number of inches by 12. For example, 18 inches = 1.5 feet. If you have a mixed measurement like 5 ft 6 in, convert the inches part to 0.5 ft and add it to 5, giving 5.5 ft.

What if my room isn’t a perfect rectangle?
Break it into smaller rectangles. For example, an L-shaped room is two rectangles. Calculate each area and add them. For a triangular section, use (base × height) / 2.

How many square feet is a 10×12 room?
10 × 12 = 120 square feet. This is a common bedroom size.

Can I use this for wall area?
Yes. Measure the length of the wall and its height from floor to ceiling. Multiply them. Subtract the area of doors and windows if you’re painting – a typical door is about 21 sq ft, a standard window about 12 sq ft.

What’s the difference between square feet and feet?
Feet measure length (one dimension). Square feet measure area (two dimensions). A room that is 10 ft by 12 ft has a perimeter of 44 ft but an area of 120 sq ft.

How do I calculate square feet from inches?
Convert each dimension to feet first, then multiply. For example, 24 inches × 36 inches = 2 ft × 3 ft = 6 sq ft. Alternatively, multiply inches and divide by 144 (since 1 sq ft = 144 sq in).

Formula used

in l | Length | ft | 12 | 0
in w | Width | ft | 10 | 0
out area | Area | sq ft | l * w | 2

Each line is one input (in, sel, list) or one result (out: label, unit, formula, decimals). How the calculators work

Method: the standard formula for this calculation, rounded as each result states. See how the calculators work or report an error.