Square Feet Calculator: How to Measure Any Area

This square footage calculator works out the area of a room or space in square feet (ft²) from its length and width, or from the diameter if it is circular. You enter the dimensions in feet and inches, and the calculator returns the total area in square feet, along with the equivalent in square yards and square meters. The result is what you need for flooring, paint, tiling, or real-estate listings.

Formula

The basic formula for a rectangle is:

Area (ft²) = Length (ft) × Width (ft)

For a circle, the formula is:

Area (ft²) = π × (Diameter/2)² or π × Radius²

Where:

• Length – the longer side of the rectangle, measured in feet (ft).
• Width – the shorter side, also in feet (ft).
• Diameter – the straight-line distance across the center of a circle, in feet.
• Radius – half the diameter, in feet.
• π (pi) – approximately 3.14159.

If your measurements include inches, convert them to feet first by dividing by 12. For example, 6 inches = 0.5 ft.

Worked Example

Using the default values from the calculator: Length = 12 ft, Width = 10 ft.

1. Multiply length by width: 12 × 10 = 120.
2. The area is 120 square feet.
3. To convert to square yards, divide by 9: 120 ÷ 9 = 13.33 sq yd.
4. To convert to square meters, multiply by 0.092903: 120 × 0.092903 = 11.15 sq m.

The calculator shows 120.00 sq ft as the main answer, with 13.33 sq yd and 11.15 sq m as secondary results.

When to Use Square Footage

Square footage is the standard unit for real estate and construction in the United States and Canada. You need it when:

• Buying or selling a home – listing prices are usually per square foot.
• Ordering flooring, carpet, or tile – materials are sold by the square foot or square yard.
• Estimating paint – one gallon covers roughly 350–400 sq ft of wall (check the can).
• Calculating HVAC needs – heating and cooling capacity is often based on square footage.
• Planning a garden or lawn – soil, mulch, and sod are sold by volume or area.

For irregularly shaped rooms, break them into rectangles, calculate each area, and add them together. For an L-shaped room, divide it into two rectangles. For a triangular section, use (base × height) / 2.

How to Measure Correctly

Accurate measurements start with the right tools and technique:

1. Use a tape measure that is at least as long as the side you are measuring. Laser distance measurers work well for large rooms.
2. Measure from wall to wall, not from baseboard to baseboard – baseboards add a few inches.
3. Measure in feet and inches. If a wall is 12 feet 6 inches, write it as 12.5 ft (since 6 ÷ 12 = 0.5).
4. Measure twice – walls are not always perfectly straight, and a small error becomes a large one over a big area.
5. For circular areas (like a round patio), measure the diameter at the widest point.

If you are measuring a room for flooring, add 5–10% extra for waste and cuts. For tile, 10–15% is common because of breakage and pattern matching.

Common Mistakes and How to Avoid Them

Even with a calculator, people often make these errors:

• Mixing units – entering length in feet and width in inches gives a wrong result. Convert everything to feet first.
• Confusing square feet with linear feet – linear feet is a straight line, square feet is area. A 10 ft × 10 ft room is 100 sq ft, not 10 sq ft.
• Forgetting to divide by 9 for square yards – there are 9 sq ft in 1 sq yd (3 ft × 3 ft).
• Rounding too early – if you round 12.5 ft to 13 ft, you add 0.5 ft to every wall, which can overestimate area by several percent.
• Not accounting for closets or alcoves – for flooring, you need to include those if you plan to cover them.

Another common misconception: square footage is not the same as “livable area” in real estate. Appraisers often exclude garages, basements (unless finished), and porches. Check local guidelines or ask a professional if you are listing a home.

Converting to Other Units

Sometimes you need the area in different units. Here are the key conversions:

• 1 square foot = 144 square inches (12 × 12).
• 1 square yard = 9 square feet.
• 1 square meter = 10.7639 square feet.
• 1 acre = 43,560 square feet.
• 1 square mile = 27,878,400 square feet (640 acres).

To convert from square feet to square meters, multiply by 0.092903. To go the other way, multiply by 10.7639. For example, a 120 sq ft room is about 11.15 sq m.

Limitations of a Simple Area Calculator

This calculator assumes perfectly straight walls and right angles. Real rooms are rarely perfect. If a room is slightly trapezoidal, the rectangle formula will be off. For accurate results in oddly shaped spaces, use a more detailed floor plan or hire a professional. Also, the calculator gives the area of the floor – if you need wall area for paint, multiply the perimeter by the ceiling height, then subtract doors and windows.

For construction, always order a little extra material. A 5% overage is standard for flooring; for tile, 10–15% is safer. The calculator does not account for waste, seams, or pattern matching.

Frequently Asked Questions

How do I calculate square footage with feet and inches?

Convert the inches to a decimal of a foot by dividing by 12. For example, 8 feet 6 inches becomes 8.5 feet (since 6/12 = 0.5). Then multiply length by width. If you have a measurement like 10 ft 3 in, it is 10.25 ft.

What is the difference between square feet and square yards?

A square yard is a larger unit: 1 square yard = 9 square feet (since 1 yard = 3 feet, and 3 × 3 = 9). To convert square feet to square yards, divide by 9. Carpet is often sold by the square yard, so you might need this conversion.

How many square feet is a 12×12 room?

A room that is 12 feet by 12 feet has an area of 144 square feet (12 × 12 = 144). This is a common bedroom size. If you are ordering flooring, add about 7–10 sq ft for waste, so order roughly 150–155 sq ft.

How do I calculate square footage of a triangle?

Use the formula: Area = (base × height) / 2. Measure the base (one side) and the height (the perpendicular distance from the base to the opposite vertex). For example, a triangle with a base of 10 ft and a height of 6 ft has an area of 30 sq ft.

Does square footage include walls?

No, square footage of a room typically refers to the floor area, measured from the inside of the walls. Wall area is calculated separately by multiplying the perimeter by the ceiling height, then subtracting openings. Real estate listings usually measure living space from the exterior walls, which can include wall thickness – this is why a house’s listed square footage may differ from the sum of its room areas.

Why does my room measure different from the listing?

Listings often use “gross living area” which includes wall thickness and may exclude certain spaces like garages or unfinished basements. Also, measurements taken by appraisers follow specific standards (like ANSI) that may differ from your own tape measure. If the difference is large, you can request a professional measurement.

Related

• Seconds to mph Converter: Speed in a Click
• Ti Formula Calculator: Solve for Ti
• Standard Deviation Formula Calculator

in len | Length | ft | 12 | 0
in wid | Width | ft | 10 | 0
out area | Area | sq ft | len * wid | 2
out yards | Area | sq yd | (len * wid) / 9 | 2
out meters | Area | sq m | (len * wid) * 0.092903 | 2