Calculating square feet is simply a way of finding the area of a space or surface. For a basic rectangle, you multiply its length by its width. The part that tends to cause confusion is everything around that simple formula: measurements may be given in feet and inches, meters, centimeters, or yards, and not every space is a perfect rectangle.
You may need to calculate square footage for a bedroom, an entire house, a piece of land, flooring, carpet, paint, a wall, a ceiling, or an oddly shaped area. The method changes slightly depending on the shape and the measurements you have.
This guide walks through those situations with practical examples so you can work out square footage without having to guess which measurements to use.
How Do You Calculate Square Feet?
For a rectangular area, the basic formula is:
Square feet = Length × Width
Both measurements should be expressed in feet before you multiply them.
For example, suppose a room is:
- 12 feet long
- 10 feet wide
The calculation is:
12 × 10 = 120 square feet
So the room has an area of 120 sq ft.
The same method works for floors, patios, rectangular plots of land, ceilings, countertops, and many other surfaces.
The important thing to remember is that square footage measures area, not the length of the sides. A room that is 12 feet long and 10 feet wide is not 22 square feet; 22 feet would be the sum of the two measurements, while 120 square feet is the area.
What if the measurements aren’t in feet?
You should convert the measurements to compatible units before calculating the area.
For example:
- 24 inches × 36 inches should be converted to feet or calculated in square inches and then converted.
- 5 meters × 4 meters can be calculated in square meters and converted to square feet.
- 12 ft 6 in should be converted to a decimal number of feet before multiplying by the width.
The conversion method you need depends on the units you started with.
How to Calculate Square Feet From Feet and Inches
This is one of the most common situations when measuring rooms because tape measures often show feet and inches rather than decimal feet.
There are 12 inches in one foot, so convert the inches portion by dividing it by 12.
Decimal feet = feet + (inches ÷ 12)
For example:
8 ft 6 in
6 ÷ 12 = 0.5
So:
8 ft 6 in = 8.5 ft
If a room measures 8 ft 6 in by 12 ft, calculate:
8.5 × 12 = 102 sq ft
The room therefore has 102 square feet.
Example with inches on both measurements
Suppose a room measures:
12 ft 6 in × 10 ft 4 in
Convert both measurements:
12 ft 6 in = 12.5 ft
10 ft 4 in = 10 + (4 ÷ 12) = 10.3333 ft
Then:
12.5 × 10.3333 ≈ 129.17 sq ft
So the area is approximately 129.17 square feet.
Avoid treating 12 ft 6 in as 12.6 feet. The “6” represents six inches, not six-tenths of a foot.
How to Calculate Square Feet of a Room
For a straightforward rectangular room, measure the inside length and width, then multiply them.
Room area = Length × Width
For example, a bedroom measuring 14 feet by 11 feet has:
14 × 11 = 154 sq ft
Square room
If all four sides are equal, you only need one side measurement.
Area = Side × Side
A room measuring 10 feet on each side has:
10 × 10 = 100 sq ft
Room measured in feet and inches
If the measurements include inches, convert them to decimal feet first.
For example:
15 ft 3 in × 11 ft 6 in
15 ft 3 in = 15.25 ft
11 ft 6 in = 11.5 ft
Then:
15.25 × 11.5 = 175.375 sq ft
The area is approximately 175.38 square feet.
What if the room isn’t rectangular?
Don’t try to force one length and one width onto an irregular room. Instead, divide the room into smaller rectangles or other simple shapes, calculate each section separately, and add the areas together.
That approach is usually easier to check and reduces the chance of overlooking a section.
How to Calculate Square Feet of an Irregular-Shaped Room
An irregular room can still be measured accurately enough for many everyday projects if you break it into simpler sections.
Imagine an L-shaped room. Instead of treating the entire outline as one complicated shape, divide it into two rectangles.
For example:
Main section:
15 ft × 10 ft = 150 sq ft
Additional section:
5 ft × 6 ft = 30 sq ft
Add them:
150 + 30 = 180 sq ft
The total area is 180 square feet.
Another method: subtract the missing section
Sometimes an irregular room is easier to calculate by imagining a complete rectangle around it and subtracting the part that is missing.
For example:
- Overall rectangle: 20 ft × 15 ft = 300 sq ft
- Missing section: 5 ft × 6 ft = 30 sq ft
Therefore:
300 − 30 = 270 sq ft
Both approaches give the same area when the measurements are consistent.
A good way to handle an irregular space
Before doing any calculations, sketch the shape on paper. It doesn’t need to be an architectural drawing. Mark each relevant length on the sketch and draw lines showing how you have divided the area.
Then:
- Calculate each simple section.
- Add sections that belong to the area.
- Subtract cutouts or missing sections.
- Check that your dimensions make sense.
For complicated property boundaries or measurements that have legal or financial consequences, an estimate from a calculator should not be treated as a professional survey.
How to Calculate Square Feet of a Square
A square has four equal sides, so its area is found by multiplying one side by itself.
Square feet = Side × Side
For example, if a square patio is 14 feet on each side:
14 × 14 = 196 sq ft
The area is 196 square feet.
Do not confuse this with the perimeter. The perimeter of that same square would be 56 feet, but its area is 196 square feet.
How to Calculate Square Feet of a Rectangle
A rectangle has two pairs of equal sides. To find its area, multiply the length by the width.
Area = Length × Width
For a 20 ft × 15 ft area:
20 × 15 = 300 sq ft
For a 16 ft × 9 ft area:
16 × 9 = 144 sq ft
It does not matter which side you call the “length” and which you call the “width.” What matters is that you multiply the two perpendicular dimensions that describe the area.
How to Calculate Square Feet From Square Meters
If your measurements or property information are given in square meters, you can convert the finished area to square feet.
The standard conversion is:
1 square meter = 10.7639 square feet
So:
Square feet = Square meters × 10.7639
For example, if a floor is 25 square meters:
25 × 10.7639 = 269.0975 sq ft
Rounded to two decimal places:
25 m² ≈ 269.10 sq ft
For the reverse conversion:
Square meters = Square feet ÷ 10.7639
NIST lists 1 square foot as 0.09290304 square meters and 1 square meter as approximately 10.7639 square feet.
How to Calculate Square Feet From Square Yards
One square yard contains exactly 9 square feet because a yard is 3 feet long and:
3 × 3 = 9
Therefore:
Square feet = Square yards × 9
For example:
20 sq yd × 9 = 180 sq ft
So 20 square yards equals 180 square feet.
To convert square feet back to square yards:
Square yards = Square feet ÷ 9
For example:
450 sq ft ÷ 9 = 50 sq yd
NIST lists one square yard as exactly 9 square feet.
How to Calculate Square Feet From Inches
If both dimensions are given entirely in inches, you can calculate the area in square inches first.
There are 144 square inches in one square foot:
12 × 12 = 144
Therefore:
Square feet = (Length in inches × Width in inches) ÷ 144
For example, suppose a sheet measures 72 inches by 48 inches:
72 × 48 = 3,456 square inches
Then:
3,456 ÷ 144 = 24 sq ft
So the sheet covers 24 square feet.
This method can be useful for countertops, sheets, panels, furniture components, and other smaller surfaces where measurements are commonly given in inches.
How to Calculate Square Feet From Centimeters
There are two practical ways to convert centimeters to square feet.
If you have the length and width in centimeters, you can first convert each dimension into feet:
Feet = Centimeters ÷ 30.48
Then multiply the two measurements.
For example, suppose a rectangular surface measures:
300 cm × 200 cm
Convert the dimensions:
300 ÷ 30.48 ≈ 9.8425 ft
200 ÷ 30.48 ≈ 6.5617 ft
Then:
9.8425 × 6.5617 ≈ 64.58 sq ft
You can also calculate the area in square centimeters first and then convert it. One square foot equals 929.0304 square centimeters.
How to Calculate Square Feet of Land
The same area principles apply to land, but plots are not always neat rectangles.
Rectangular land
If a plot measures 50 feet by 80 feet:
50 × 80 = 4,000 sq ft
The plot has 4,000 square feet.
Square plot
If a square plot has sides of 60 feet:
60 × 60 = 3,600 sq ft
Irregular plot
For an irregular plot, divide the land into rectangles, triangles, or other shapes whose areas you can calculate. Add the individual sections together.
Land records and property listings may also use acres, square yards, hectares, or regional units rather than square feet. Make sure you know which unit is being used before comparing two areas.
One acre contains exactly 43,560 square feet. An acre does not have to be square or rectangular; it is a unit of area, not a required shape.
For a property purchase, boundary dispute, construction permit, or other situation where exact legal dimensions matter, use the relevant property records or a qualified surveyor rather than relying on an approximate measurement.
How to Calculate Square Feet of a House
Calculating the area of an entire house is different from measuring one room.
Start by separating the house into measurable areas. For example, you might have:
- Living room
- Bedrooms
- Kitchen
- Hallways
- Bathrooms
- Other enclosed areas
Calculate each section individually and add them together.
Suppose the areas are:
| Area | Square feet |
|---|---|
| Living room | 400 sq ft |
| Kitchen | 120 sq ft |
| Bedrooms | 300 sq ft |
| Other included areas | 180 sq ft |
| Total | 1,000 sq ft |
The combined area is therefore 1,000 square feet.
Be careful when using a floor plan. An area that is already included inside a larger measurement should not be added again.
Also, “square footage” can have a specific meaning in property listings, construction documents, and appraisals. The exact area being reported may depend on the measurement convention being used, so don’t assume that every advertised square-foot figure was calculated from exactly the same boundaries.
How to Calculate Square Feet of Multiple Rooms
When measuring several rooms, calculating each room separately is usually the cleanest approach.
For example:
| Room | Length | Width | Area |
|---|---|---|---|
| Bedroom | 12 ft | 10 ft | 120 sq ft |
| Living room | 18 ft | 14 ft | 252 sq ft |
| Kitchen | 10 ft | 8 ft | 80 sq ft |
Then add the areas:
120 + 252 + 80 = 452 sq ft
The three rooms have a combined area of 452 square feet.
This approach also makes mistakes easier to find. If the final number seems wrong, you can check each room instead of measuring the entire property again.
How to Calculate Square Feet for Flooring
For a rectangular floor, calculate:
Length × Width = floor area
If the floor is 16 ft × 12 ft:
16 × 12 = 192 sq ft
So the floor itself covers 192 square feet.
For multiple rooms, calculate each room and add the results.
How much extra flooring should you buy?
The amount of material you need to purchase is not always exactly the same as the floor’s measured area.
You may need additional material because of:
- Cuts around walls and corners
- Room shape
- Pattern matching
- Direction of installation
- Damaged or unusable pieces
- Installation method
The appropriate allowance varies by product and project. Rather than treating one percentage as a universal rule, check the flooring manufacturer’s or installer’s recommendation.
The distinction is important:
Measured floor area = space you need to cover
Material purchased = area to cover + project-specific cutting/waste allowance
How to Calculate Square Feet for Carpet
The basic floor-area calculation is the same:
Length × Width
However, buying carpet is not always as simple as buying exactly the number of square feet calculated.
Carpet is supplied in particular roll widths, and the layout of the room can determine how pieces need to be cut and joined.
For example, a 10 ft × 12 ft room has:
10 × 12 = 120 sq ft
But that does not automatically mean you can order exactly 120 square feet of carpet and have no leftover material. The roll width, seams, orientation, pattern, and cutting plan can change the amount required.
For carpet installation, use the square-foot calculation as the starting point and then determine the actual material requirement from the product’s available dimensions and the installation layout.
How to Calculate Square Feet for Paint
Paint calculations are different because you are usually measuring wall surface area, not floor area.
For a rectangular room, calculate the area of each wall:
Wall area = Wall length × Wall height
For example, one wall that is 15 feet long and 8 feet high has:
15 × 8 = 120 sq ft
Do the same for the other walls and add them together.
Subtract doors and windows
If you’re estimating the surface that actually needs paint, subtract large openings such as doors and windows from the total wall area.
For example:
Total wall area = 480 sq ft
Doors and windows = 50 sq ft
Paintable wall area = 430 sq ft
The amount of paint you ultimately need will also depend on the paint’s stated coverage, the number of coats, the surface condition, and application method. Square footage gives you the surface area; it does not by itself determine the number of gallons or liters required.
How to Calculate Square Feet of a Wall
For a rectangular wall:
Wall area = Length × Height
A wall that is 12 feet long and 8 feet high has:
12 × 8 = 96 sq ft
So its surface area is 96 square feet.
If the wall contains a door or large window and you’re calculating paint, wallpaper, paneling, or tile requirements, measure those openings separately and subtract their area.
For example:
96 sq ft wall
minus
21 sq ft door
equals:
75 sq ft of remaining wall area
How to Calculate Square Feet of a Ceiling
For a rectangular ceiling, use the same formula as a floor:
Ceiling area = Length × Width
A ceiling measuring 20 feet by 15 feet has:
20 × 15 = 300 sq ft
For a ceiling with an unusual shape, divide it into smaller rectangles or other simple shapes and add their areas.
Do not use the room’s perimeter to calculate ceiling area. The ceiling covers the horizontal surface above the room, so its area is based on its length and width.
How to Calculate Square Feet of a Triangle
For a triangle, use:
Area = (Base × Height) ÷ 2
The height must be the perpendicular distance from the base to the opposite point. It is not necessarily the length of one of the sloping sides.
For example, if a triangle has:
- Base = 12 ft
- Height = 8 ft
Then:
(12 × 8) ÷ 2 = 48 sq ft
The triangle has an area of 48 square feet.
This formula is useful when an irregular room, garden, roof section, or land parcel contains a triangular portion.
How to Calculate Square Feet of a Circle
For a circular area, use:
Area = π × radius²
The radius is the distance from the center of the circle to its edge.
If the diameter is given, divide it by 2 to get the radius.
For example, if a circular patio has a radius of 5 feet:
π × 5²
= π × 25
≈ 78.54 sq ft
So the circular area is approximately 78.54 square feet.
A common mistake is using the diameter where the formula requires the radius. If the diameter is 10 feet, the radius is 5 feet.
How to Calculate Square Feet of a Semicircle
A semicircle is half of a circle, so its area is:
Area = (π × radius²) ÷ 2
If the radius is 6 feet:
(π × 6²) ÷ 2
≈ 56.55 sq ft
The semicircle has approximately 56.55 square feet of area.
If you are given the diameter instead, divide it by 2 before using the formula.
How to Calculate Square Feet of a Trapezoid
For a trapezoid, use:
Area = ((Base 1 + Base 2) × Height) ÷ 2
Suppose the two parallel sides are:
- Base 1 = 10 ft
- Base 2 = 16 ft
- Height = 8 ft
Then:
((10 + 16) × 8) ÷ 2
= 104 sq ft
So the trapezoid has an area of 104 square feet.
The height in this formula means the perpendicular distance between the two parallel bases, not the length of either sloping side.
How to Calculate Square Feet When the Shape Is Irregular
There is no single length × width formula that works for every irregular shape.
The practical solution is to break the area into shapes whose areas you know how to calculate.
For example, an irregular patio might contain:
- One rectangle
- One triangle
- One small rectangle
Calculate each:
Rectangle = 150 sq ft
Triangle = 24 sq ft
Small rectangle = 30 sq ft
Then:
150 + 24 + 30 = 204 sq ft
For a shape with a cutout, calculate the larger area and subtract the area of the missing section.
The more complicated the outline becomes, the more important it is to make a sketch and label every measurement before calculating.
Square Feet Conversion Chart
Here are some of the most useful area conversions:
| Area unit | Equivalent |
|---|---|
| 1 square inch | 0.00694444 sq ft |
| 1 square foot | 1 sq ft |
| 1 square yard | 9 sq ft |
| 1 square meter | 10.7639 sq ft |
| 1 acre | 43,560 sq ft |
| 1 hectare | 107,639.1 sq ft |
NIST lists 144 square inches in one square foot, 9 square feet in one square yard, approximately 10.7639 square feet in one square meter, and exactly 43,560 square feet in one acre.
These conversions are useful when comparing measurements from different sources. Always make sure you’re converting area to area. Converting 10 feet to meters is not the same operation as converting 10 square feet to square meters.
Square Feet vs Other Area Measurements
Square feet vs feet
A foot (ft) measures length.
A square foot (sq ft or ft²) measures area.
For example, a wall might be 12 feet long, while a 12 ft × 10 ft floor has an area of 120 square feet.
Square feet vs square yards
A square yard is larger:
1 sq yd = 9 sq ft
So 90 square feet is:
90 ÷ 9 = 10 square yards
Square feet vs square meters
A square meter is larger than a square foot:
1 m² ≈ 10.7639 sq ft
Therefore, 100 square meters is approximately:
100 × 10.7639 = 1,076.39 sq ft
Square feet vs acres
An acre is a much larger unit commonly used for land:
1 acre = 43,560 sq ft
An acre does not have to be a particular shape. It represents a fixed amount of area.
Square feet vs cubic feet
These units measure different things.
Square feet = area
Cubic feet = volume
A 10 ft × 10 ft floor has an area of 100 square feet. If that space is 8 feet high, the enclosed volume would be 800 cubic feet.
Do not use cubic feet when you are trying to calculate the surface area of a floor, wall, or plot.
Common Mistakes When Calculating Square Feet
Most square-footage mistakes are not caused by difficult mathematics. They usually happen because the measurements were interpreted incorrectly.
Adding dimensions instead of multiplying them
If a room is 12 ft × 10 ft, adding the measurements gives 22 feet, not 120 square feet.
Treating inches as decimal feet
6 inches is 0.5 feet, not 0.6 feet.
Convert inches by dividing by 12.
Mixing units
Multiplying 12 feet by 36 inches without converting one of the measurements first will produce the wrong result.
Using diameter instead of radius
For a circle, the formula uses radius. If the diameter is 10 feet, the radius is 5 feet.
Forgetting part of an irregular area
An L-shaped room can easily be underestimated if only its largest rectangle is measured.
Counting the same space twice
This can happen when adding several sections of a floor plan, especially around hallways and open-plan rooms.
Confusing wall area with floor area
A 12 ft × 10 ft room has 120 square feet of floor area, but its total wall surface is calculated using wall lengths and wall height.
Relying on rough measurements for a precision project
A few inches can make a meaningful difference when you’re ordering expensive materials or working with a large area. For those projects, measure carefully and verify the dimensions before placing an order.
How to Measure a Room for Square Footage
You don’t need complicated equipment to measure a simple room.
What you need
A basic measuring tape is enough for many rooms. A laser distance measurer can make longer distances easier to measure, but it isn’t essential.
You’ll also want something to record the measurements and a simple sketch of the room.
Step 1: Draw the room
Sketch the floor from above. It does not need to be to scale.
Mark doors, alcoves, recesses, corners, or other parts that affect the shape.
Step 2: Measure each relevant dimension
For a rectangular room, measure the length and width.
For an irregular room, measure enough sections to divide it into simple shapes.
Step 3: Record feet and inches clearly
Write something like:
12 ft 7 in
rather than writing “12.7 ft” unless you have already converted the measurement.
Step 4: Double-check your measurements
If the room is supposed to be rectangular, the dimensions of opposite sides should make sense relative to each other. If they differ, don’t automatically assume one measurement is correct.
Step 5: Calculate each section
Use the appropriate formula for each shape.
Step 6: Add or subtract areas
Combine the sections that make up the space and subtract any areas that are excluded.
For a straightforward project, this method is usually enough to produce a useful square-foot estimate.
How to Calculate Square Feet for Materials
Square footage is often the first calculation needed when estimating materials, but it is not necessarily the final quantity you should purchase.
The same basic area calculation can be used for:
- Flooring
- Tile
- Carpet
- Paint
- Wallpaper
- Wall panels
- Siding
- Countertops
- Other sheet or surface materials
The next step depends on the material.
For flooring, cutting and installation patterns can create waste.
For tile, the layout, grout joints, cuts, and breakage can affect the amount required.
For paint, coverage depends on the product, surface, number of coats, and application conditions.
For carpet, roll width and seam placement matter.
So use the calculated square footage as the starting area, then follow the product’s coverage information and installation guidance to determine the amount to purchase.
How Many Square Feet Do I Need?
The answer depends on what you are measuring.
For a floor
Multiply length by width.
For a ceiling
Multiply ceiling length by width.
For a rectangular wall
Multiply wall length by wall height.
For multiple rooms
Calculate each room separately and add the results.
For an irregular area
Divide the space into simpler shapes, calculate each one, and combine the results.
For flooring, carpet, tile, or other materials
First calculate the area to be covered. Then account for the product dimensions, cutting requirements, installation pattern, and recommended allowance for waste.
This distinction matters because ordering material based solely on the exact measured area can leave you short once cuts and unusable pieces are taken into account.
Worked Square-Foot Examples
Example 1: 10 × 12 room
10 × 12 = 120 sq ft
The room has 120 square feet.
Example 2: 15 × 20 room
15 × 20 = 300 sq ft
The room has 300 square feet.
Example 3: 12 ft 6 in × 10 ft
Convert 12 ft 6 in:
12 + 6/12 = 12.5 ft
Then:
12.5 × 10 = 125 sq ft
Example 4: 20 square meters
20 × 10.7639 = 215.278 sq ft
So:
20 m² ≈ 215.28 sq ft
Example 5: L-shaped area
Main rectangle:
15 × 10 = 150 sq ft
Additional rectangle:
5 × 6 = 30 sq ft
Total:
150 + 30 = 180 sq ft
Example 6: Circular patio
Radius = 5 ft
π × 5² ≈ 78.54 sq ft
The patio has approximately 78.54 square feet of area.
Related Calculators and Guides
Once you know the area you’re working with, you may need a different calculation depending on the project. Relevant tools can help with area measurements, unit conversions, flooring quantities, paint coverage, and other calculations where square footage is only one part of the answer.