How to Calculate Square Feet
Calculate square feet instantly. Simple formulas for rectangles, circles, triangles, and irregular rooms. Use our calculator or follow the step-by-step method.
How to Calculate Square Feet
To calculate square feet, multiply the length by the width, measured in feet:
Square Feet = Length (ft) × Width (ft)
For example, a room that is 12 feet long and 10 feet wide has an area of:
12 × 10 = 120 ft²
So the room is 120 square feet.
If your measurements include inches, convert the inches to a fraction or decimal of a foot before multiplying.
Square Footage Calculator Formula
For any rectangular or square area, use:
A = L × W
Where:
A= area in square feetL= length in feetW= width in feet
Example: 15 ft × 12 ft Room
15 × 12 = 180
The room measures:
180 sq ft
The same formula works for rectangular floors, rooms, patios, lawns, walls, countertops, and other flat surfaces.
How to Calculate Square Feet With Feet and Inches
Measurements are not always exact whole feet. You might measure a room as 12 ft 6 in by 10 ft 3 in.
Before calculating the area, convert the inches to feet.
Since:
12 inches = 1 foot
use:
Decimal feet = Feet + Inches/12
Example: 12 ft 6 in × 10 ft 3 in
Convert the first measurement:
12 + 6/12 = 12.5 ft
Convert the second:
10 + 3/12 = 10.25 ft
Now multiply:
12.5 × 10.25 = 128.125
The area is approximately:
128.13 sq ft
For most home projects, you can round the final area to a practical level of precision after completing the calculation.
What Is a Square Foot?
A square foot is a unit of area.
One square foot represents a square measuring:
1 ft × 1 ft
So:
1 ft × 1 ft = 1 ft²
Square footage measures the size of a surface rather than its perimeter or volume.
It is commonly used for:
- rooms and floor space
- flooring
- walls and paintable surfaces
- patios and decks
- lawns and landscaping
- countertops
- property and land area
How to Measure a Room in Square Feet
For a rectangular room:
- Measure the room’s length.
- Measure its width.
- Convert both measurements to feet if necessary.
- Multiply length by width.
For example:
Length: 20 ft
Width: 15 ft
20 × 15 = 300 sq ft
The room has 300 square feet of floor area.
Measure the actual surface you need rather than assuming that every wall or corner is perfectly straight.
How to Calculate Square Feet of an Irregular Room
An irregular or L-shaped room can usually be divided into simple shapes.
The easiest approach is to break the floor plan into rectangles, calculate each rectangle separately, and add the results.
Example: L-Shaped Room
Suppose the room can be divided into:
Section A: 20 ft × 15 ft = 300 sq ft
Section B: 10 ft × 8 ft = 80 sq ft
Add the two areas:
300 + 80 = 380
The total floor area is:
380 sq ft
Subtracting a Cutout
Sometimes it is easier to calculate one large rectangle and subtract an area that is not part of the room.
For example:
Full rectangle: 25 ft × 20 ft = 500 sq ft
Cutout: 5 ft × 4 ft = 20 sq ft
Then:
500 - 20 = 480
The actual area is:
480 sq ft
Use whichever method produces simpler measurements.
How to Calculate Square Feet of a Wall
For a rectangular wall:
Wall Area = Width × Height
For example, a wall that is 15 feet wide and 10 feet high has an area of:
15 × 10 = 150 sq ft
For several walls, calculate each wall and add the areas together.
Example: Four Walls in a Room
A room measures 15 ft × 12 ft with a 10 ft ceiling.
Two walls are:
15 × 10 = 150 sq ft each
Together:
150 × 2 = 300 sq ft
The other two walls are:
12 × 10 = 120 sq ft each
Together:
120 × 2 = 240 sq ft
Total wall area:
300 + 240 = 540 sq ft
If you need the paintable area rather than total wall area, you can subtract doors, windows, or other large surfaces that will not be painted.
How to Calculate Square Feet of a Circle
For a circular area, use:
A = π r²
Where r is the radius.
The radius is half the diameter.
Example: 10 ft Diameter Patio
Diameter:
10 ft
Radius:
10 ÷ 2 = 5 ft
Calculate the area:
π × 5² ≈ 78.54
The patio is approximately:
78.54 sq ft
How to Calculate Square Feet of a Triangle
For a triangle:
A = (b × h)/2
Where:
b= baseh= perpendicular height
Example
For a triangle with a 12 ft base and an 8 ft perpendicular height:
(12 × 8)/2 = 48
The area is:
48 sq ft
Make sure the height is measured perpendicular to the base rather than along a sloping side.
Square Feet Conversion Chart
These are common area conversions:
| Convert | Formula |
|---|---|
| Square inches → square feet | Divide by 144 |
| Square yards → square feet | Multiply by 9 |
| Square meters → square feet | Multiply by about 10.764 |
| Square feet → square inches | Multiply by 144 |
| Square feet → square yards | Divide by 9 |
| Square feet → square meters | Multiply by 0.09290304 |
| Acres → square feet | Multiply by 43,560 |
| Square feet → acres | Divide by 43,560 |
The National Institute of Standards and Technology (NIST) lists the conversion from one square foot to one square meter as 0.09290304 m².
Source: NIST Guide to the SI — Conversion Factors
Square Inches to Square Feet
There are:
144 square inches = 1 square foot
This is because:
12 in × 12 in = 144 in²
To convert square inches to square feet:
Square Feet = Square Inches/144
For example:
1,728 ÷ 144 = 12
So:
1,728 in² = 12 ft²
Square Yards to Square Feet
One square yard contains:
9 square feet
because:
1 yard = 3 feet
and:
3 ft × 3 ft = 9 ft²
Therefore:
Square Feet = Square Yards × 9
For example:
20 × 9 = 180
So:
20 yd² = 180 ft²
Square Meters to Square Feet
One square meter is approximately:
10.764 square feet
To convert:
Square Feet = Square Meters × 10.764
For example:
25 × 10.764 ≈ 269.1
So:
25 m² ≈ 269.1 ft²
For the reverse conversion:
Square Meters = Square Feet × 0.09290304
NIST publishes official U.S.–SI conversion factors for these units.
Source: NIST Approximate U.S. Customary to Metric Conversions
Acres to Square Feet
One acre contains:
43,560 square feet
So:
Square Feet = Acres × 43,560
Common examples:
| Acres | Square Feet |
|---|---|
| 0.25 acre | 10,890 sq ft |
| 0.5 acre | 21,780 sq ft |
| 1 acre | 43,560 sq ft |
| 2 acres | 87,120 sq ft |
Calculating Square Feet for Flooring
For a rectangular floor, first calculate:
Floor Area = Length × Width
Suppose a room measures:
20 ft × 15 ft
The floor area is:
20 × 15 = 300 sq ft
If the flooring package states that each box covers 20 sq ft, the theoretical number of boxes is:
300 ÷ 20 = 15
In practice, flooring projects often require additional material for cuts, layout, defects, and future repairs.
Do not assume one waste percentage applies to every flooring product. Check the manufacturer’s installation instructions and account for the room layout before ordering.
Calculating Square Feet for Paint
For walls, calculate the width × height of each wall and add the results.
Suppose the total wall area is:
540 sq ft
and you have:
Door: 3 ft × 7 ft = 21 sq ft
Two windows: 3 ft × 4 ft each = 24 sq ft total
Subtract those openings if they will not be painted:
540 - 21 - 24 = 495
The estimated paintable area is:
495 sq ft
Paint coverage depends on the product, surface, application method, and number of coats. As a general reference point, an EPA technical document uses approximately 400 sq ft per gallon as a rule-of-thumb coverage value while explicitly noting that actual coverage can vary.
Source: U.S. EPA — Technical Guidance
For an actual project, use the coverage stated on the specific paint manufacturer’s label rather than relying solely on a general estimate.
Calculating Square Feet for Landscaping
For a rectangular lawn:
Area = Length × Width
Suppose a yard measures:
40 ft × 30 ft
Total area:
40 × 30 = 1,200 sq ft
If a 20 ft × 20 ft patio occupies part of that area:
20 × 20 = 400 sq ft
Subtract the patio:
1,200 - 400 = 800
The lawn area is:
800 sq ft
If you are ordering sod, seed, mulch, or another material, use the coverage information supplied by the specific manufacturer or supplier.
Measurement Tips for More Accurate Results
Use Consistent Units
Do not multiply feet by inches.
Convert both dimensions to the same unit first. For square feet, converting everything to feet before multiplying is usually easiest.
Measure Each Section
Irregular rooms are easier to calculate accurately when divided into simple rectangles or other basic shapes.
Record Measurements as You Go
Write down each dimension immediately. For complicated spaces, sketching the floor plan and labeling each measurement can prevent sections from being missed or counted twice.
Measure the Surface You Actually Need
Floor area, wall area, ceiling area, and property area are different measurements.
For example, the square footage of a room’s floor does not tell you how many square feet of wall need to be painted.
Check Product Coverage Before Ordering
Flooring boxes, paint, sod, tile, and other materials can have different coverage rates and installation requirements.
Calculate the physical area first, then apply the product-specific coverage and waste requirements.
Common Square Footage Mistakes
Multiplying Feet by Inches
This produces mixed units rather than square feet.
Convert inches to feet first.
Adding Length and Width
Square footage measures area, so you multiply:
Length × Width
Adding the sides calculates part of the perimeter instead.
Forgetting Irregular Sections
Alcoves, extensions, closets, islands, patios, and other sections can change the total area.
Break the space into manageable shapes and calculate them individually.
Confusing Linear Feet With Square Feet
A linear foot measures length.
A square foot measures area.
For example:
12 linear ft = a length of 12 ft
12 sq ft = an area totaling 12 ft²
You cannot directly convert linear feet to square feet without knowing another dimension, such as width.
Rounding Too Early
Keep reasonable precision while calculating and round the final result.
This is particularly useful when converting inches to decimal feet.
Quick Square Footage Reference
| Shape | Formula |
|---|---|
| Rectangle | Length × Width |
| Square | Side × Side |
| Triangle | (Base × Height) ÷ 2 |
| Circle | π × Radius² |
| Irregular room | Divide into shapes and add the areas |
For a standard rectangular room:
12 ft × 10 ft = 120 sq ft
For measurements containing inches:
12 ft 6 in = 12.5 ft
Then use the normal area formula.
Frequently Asked Questions
How do you calculate square feet?
For a rectangular space, measure the length and width in feet and multiply them:
Square Feet = Length × Width
A 12 ft × 10 ft room is therefore 120 sq ft.
How do I calculate square feet when measurements include inches?
Convert the inches to feet by dividing by 12, add that value to the whole feet, and then multiply the two dimensions.
For example:
10 ft 6 in = 10.5 ft
How many square feet are in a 10 × 10 room?
10 × 10 = 100
A 10 ft × 10 ft room contains 100 sq ft.
How many square feet are in a 12 × 12 room?
12 × 12 = 144
A 12 ft × 12 ft room contains 144 sq ft.
How many square feet are in a 20 × 20 room?
20 × 20 = 400
A 20 ft × 20 ft room contains 400 sq ft.
How do I calculate square footage for an L-shaped room?
Divide the L shape into two rectangles. Calculate length × width for each rectangle, then add the two areas.
How do I calculate wall square footage?
Multiply each wall’s width by its height, then add the wall areas together.
If necessary, subtract doors, windows, or other areas that will not be covered.
Is 1 square foot the same as 12 inches?
No.
One linear foot equals 12 inches, but one square foot equals:
12 in × 12 in = 144 in²
How many square feet are in an acre?
There are 43,560 square feet in one acre.
How many square feet are in a square meter?
One square meter is approximately 10.764 square feet.
What’s the difference between square feet and feet?
Feet measure length.
Square feet measure area.
For example, a board might be 8 feet long, while a room might have an area of 120 square feet.
Related Calculator
For checking room, wall, flooring, or landscaping area estimates, use the Square Foot Calculator.
Conclusion
For most spaces, calculating square feet comes down to one formula:
Square Feet = Length × Width
Measure both dimensions in feet, multiply them, and the result is the area in square feet.
For measurements containing inches, convert the inches to feet first. For irregular spaces, divide the area into simple shapes and add the results. Circles and triangles require their own area formulas, but the principle is the same: measure the dimensions accurately and calculate the area of the surface you actually need.
When using the result to buy flooring, paint, landscaping materials, or other products, calculate the area first and then follow the specific manufacturer’s coverage and waste recommendations.