Square Footage Calculator: How to Calculate Sq Ft

This calculator works out the square footage of a rectangular room or area from its length and width in feet, and also gives the result in square yards and square meters. You enter the length and width in feet, and you get the area in square feet, square yards, and square meters. It is a straightforward length × width calculation, with automatic unit conversions included.

Formula

The formula for square footage of a rectangle is:

Area (ft²) = Length (ft) × Width (ft)

Where:

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

To convert to square yards, divide by 9 (since 1 yd² = 9 ft²). To convert to square meters, multiply by 0.09290304 (since 1 ft² = 0.09290304 m²).

Worked Example

Using the default values from the calculator (length = 40 ft, width = 25 ft):

1. Area in square feet: 40 × 25 = 1000 ft²
2. Area in square yards: 1000 ÷ 9 = 111.11 yd² (rounded to 2 decimals)
3. Area in square meters: 1000 × 0.09290304 = 92.90 m² (rounded to 2 decimals)

These match the calculator outputs exactly.

When to Use Square Footage

Square footage is the standard unit for floor area in the United States and Canada. You will need it for:

• Buying or selling a home – listing agents quote price per square foot.
• Ordering flooring, tile, or carpet – you need the area to estimate material quantities.
• Painting walls – though walls are measured differently (see below).
• Heating and cooling load estimates – HVAC professionals use square footage as a starting point.
• Fertilizer or seed application – for lawns, you need the area in square feet or square yards.

For irregular shapes, break the space into rectangles, calculate each, and add them together. For a triangle, use (base × height) ÷ 2. For a circle, use π × radius².

How to Measure a Room Correctly

To get accurate square footage, follow these steps:

1. Clear the floor along the walls so you can measure from baseboard to baseboard.
2. Use a tape measure that is at least as long as the wall. For large rooms, use a laser distance measurer.
3. Measure the length and width in feet and inches. Convert inches to decimal feet by dividing by 12 (e.g., 6 inches = 0.5 ft).
4. Multiply length × width.
5. If the room is not a perfect rectangle, divide it into rectangles, measure each, and sum the areas.

For example, a room that is 12 ft 6 in by 10 ft 3 in becomes 12.5 ft × 10.25 ft = 128.125 ft².

Common Mistakes and How to Avoid Them

Even experienced DIYers make these errors:

• Mixing units – measuring one side in feet and the other in inches. Always convert to the same unit first.
• Forgetting to subtract obstructions – for flooring, you should measure the open floor area, not the full room dimensions if there are permanent fixtures like kitchen islands. However, for real estate listings, you typically measure the exterior walls.
• Rounding too early – if you round each measurement to the nearest foot, you can lose accuracy. Keep decimals until the final answer.
• Confusing square feet with linear feet – square feet is an area, linear feet is a length. A 10 ft × 10 ft room is 100 ft², not 20 ft².
• Forgetting to convert inches to feet – 12 inches = 1 foot, so 6 inches = 0.5 ft. A common error is treating inches as a decimal of a foot directly (e.g., 6 inches as 0.6 ft), which is wrong.

Square Footage vs. Other Area Units

Square footage is not the only area unit you will encounter:

• Square yards – often used for carpet and sod. 1 yd² = 9 ft².
• Square meters – the metric standard. 1 m² ≈ 10.764 ft².
• Acres – for large land areas. 1 acre = 43,560 ft².
• Hectares – 1 ha = 10,000 m² ≈ 107,639 ft².
• Square inches – for small surfaces. 1 ft² = 144 in².

When comparing prices, always check the unit. A carpet priced per square yard will seem cheaper than per square foot, but you need to compare the same unit.

Limitations of the Rectangle Formula

This calculator assumes a perfect rectangle. Real rooms often have alcoves, closets, or angled walls. For those, you need to break the space into smaller rectangles or triangles. Also, the formula gives the floor area, not the wall area. To paint walls, you need to measure the perimeter × height, minus windows and doors.

For irregular shapes, the rectangle formula will over- or under-estimate. The more irregular the shape, the more segments you should divide it into. For a professional appraisal, a licensed appraiser uses specific measurement standards (ANSI Z765) that include only finished, heated areas.

Frequently Asked Questions

How do I calculate square footage from inches?

First convert inches to feet by dividing by 12, then multiply length × width. For example, a 120-inch by 60-inch area is 10 ft × 5 ft = 50 ft².

What is the difference between square footage and square meters?

Square feet and square meters are both units of area. 1 square meter equals about 10.764 square feet. To convert from square feet to square meters, multiply by 0.09290304.

How many square feet is a 20×20 room?

A room that is 20 feet long and 20 feet wide has an area of 400 square feet (20 × 20 = 400).

Do I include closets in square footage?

In most real estate listings, yes – closets are included in the finished square footage. However, some appraisals may exclude them if they are not finished. For flooring, you should measure the actual floor area including closets if you plan to cover them.

How do I calculate square footage of a triangle?

Multiply the base by the height and divide by 2. For example, a triangle with a base of 10 ft and height of 6 ft has an area of 30 ft².

What is the formula for square footage of a circle?

Use π × radius². If the radius is 5 ft, the area is π × 25 ≈ 78.54 ft².

Related

• Land Area Calculator Online: How to Measure Any Plot
• Land Area of City Calculator: How to Estimate
• Km to Acres Calculator: Convert Quickly

in l | Length | ft | 40 | 0 | 100000
in w | Width | ft | 25 | 0 | 100000
out sqft | Area | ft² | l * w | 2
out syd | Area | yd² | l * w / 9 | 2
out sm | Area | m² | l * w * 0.09290304 | 2