Use this calculator to measure any room, floor or lot in square feet, square meters and square yards. Handles rectangles, circles, triangles, L-shapes and irregular areas, with a live multi-room tally, perimeter for trim and skirting, waste buffer, and cost per square foot.
- 5 Shape Types
- Multi-Room Tally
- Metric and Imperial
- Perimeter for Trim
- Waste Buffer
- Cost Estimate
Multi-room project tally ▾
Measuring a whole house or a multi-room renovation? Add each room here. The total square footage sums live and applies the same waste buffer.
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Pick a shape, enter the dimensions, then press Calculate Square Footage.
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Unit conversions
What Is Square Footage
Square footage is a measure of area expressed in square feet. One square foot is a square measuring one foot on every side, so it is 12 inches by 12 inches, or 144 square inches. Square footage is the standard unit of area used in the United States for residential and commercial real estate, flooring, roofing, painting and landscaping.
Square footage is not a length. It is a two-dimensional measurement of how much flat space a surface covers. That distinction matters because flooring, paint and roofing are all priced per square foot of surface area, not per linear foot of edge. When you see a house listed as 2,000 square feet, that number describes the total floor area inside the walls, not the perimeter or the volume.
In metric countries the equivalent measure is square meters. One square foot equals roughly 0.0929 square meters, and one square meter equals about 10.76 square feet. The calculator above outputs both so you can work in either system without conversion tables.
To calculate the volume of bulk materials like mulch or gravel, use our calculator for cubic yards and cubic meters.
How to Calculate Square Footage
The method is simple. Measure the length and width of the area in feet. Multiply them together. That product is the square footage.
For a rectangular room 12 feet long and 10 feet wide, the calculation is 12 times 10, which equals 120 square feet. For an L-shaped room, split the shape into two rectangles, calculate each one separately, then add them. For a circular patio, measure the diameter, divide by two to get the radius, then square the radius and multiply by pi, which is about 3.1416.
When your measurements are in inches, meters, centimeters or yards, convert everything to feet first. The calculator above handles that for you, but the underlying rule is worth remembering. Inches divide by 12. Meters divide by 0.3048. Centimeters divide by 30.48. Yards multiply by 3. Once every dimension is in feet, the multiplication and addition steps are the same as they would be for a feet-only calculation.
Square Footage Formulas by Shape
The shape of the surface determines the formula. The list below covers the five shapes you will hit most often in residential and light commercial work.
| Shape | Formula | Example | Result |
|---|---|---|---|
| Rectangle | Length x Width | 12 ft x 10 ft | 120 sq ft |
| Circle | pi x radius squared | Radius 5 ft | 78.54 sq ft |
| Triangle | 0.5 x Base x Height | Base 16 ft, height 10 ft | 80 sq ft |
| L-Shape | Main rectangle plus wing rectangle | 20x10 plus 10x8 | 280 sq ft |
| Trapezoid | 0.5 x (a plus b) x height | a=10, b=6, h=8 | 64 sq ft |
For an L-shape, the wing rectangle often overlaps the main rectangle. Subtract the overlapping area or split the shape into two non-overlapping rectangles before adding. The calculator above does this automatically by asking for the two rectangles separately and adjusting for overlap.
Typical Room Sizes and Square Footage
These are the standard room sizes used in residential planning. They help you sanity-check a measurement or estimate a project before you have exact numbers.
| Room | Typical size | Square footage | Notes |
|---|---|---|---|
| Small bedroom | 10 x 10 ft | 100 sq ft | Minimum for a single bed |
| Standard bedroom | 12 x 12 ft | 144 sq ft | Fits a double bed with clearance |
| Master bedroom | 14 x 16 ft | 224 sq ft | Fits a king bed and seating |
| Living room | 16 x 20 ft | 320 sq ft | Standard family living space |
| Kitchen | 10 x 12 ft | 120 sq ft | Galley or single-wall layout |
| Open plan kitchen and living | 20 x 25 ft | 500 sq ft | Combined modern layout |
| Dining room | 12 x 14 ft | 168 sq ft | Seats six comfortably |
| Bathroom | 5 x 8 ft | 40 sq ft | Half bath minimum |
| Full bathroom | 8 x 10 ft | 80 sq ft | Tub, toilet and sink |
| Garage (single car) | 12 x 22 ft | 264 sq ft | Standard single bay |
| Garage (double car) | 22 x 22 ft | 484 sq ft | Fits two vehicles and storage |
| Home office | 10 x 12 ft | 120 sq ft | Desk, chair and shelving |
Square Footage for Flooring, Paint and Materials
Every material has its own coverage rate, and every project has its own waste factor. The area is the same. What changes is how much material you buy and how you round up to the nearest box, bucket or bundle.
| Material | Sold by | Typical coverage | Recommended waste |
|---|---|---|---|
| Laminate flooring | Box | 20 to 30 sq ft per box | 10% |
| Hardwood flooring | Box | 18 to 24 sq ft per box | 10% |
| Vinyl plank | Box | 20 to 30 sq ft per box | 10% |
| Ceramic tile | Box | 8 to 15 sq ft per box | 10 to 15% |
| Porcelain tile | Box | 8 to 15 sq ft per box | 10 to 15% |
| Carpet | Roll or square yard | Price per square yard | 5 to 10% |
| Interior paint | Gallon | 350 to 400 sq ft per coat | 5% |
| Exterior paint | Gallon | 250 to 350 sq ft per coat | 10% |
| Concrete | Cubic yard | Area times thickness | 5 to 10% |
| Roofing shingles | Bundle or square | 100 sq ft per square | 10% |
Flooring and paint waste goes up sharply when the layout has angles, patterns or repeat matches. A straight plank floor in a rectangular room wastes about 5 to 8% on cuts. A diagonal plank floor in the same room wastes 12 to 15%. Tiles with a running bond pattern waste more than a straight grid. Add the waste buffer before you order, not after you run out.
Common Square Footage Mistakes
Mixing units in one formula
Length in feet and width in inches will produce a wrong answer every time. Convert every dimension to the same unit before multiplying. The calculator above does this automatically, but on paper it is the most common arithmetic error in construction estimating.
Forgetting to subtract openings
Doors, windows, fireplaces and built-in cabinets all reduce the usable wall or floor area. On a wall of 200 square feet with a door of 21 square feet and a window of 15 square feet, the paintable area is 164 square feet, not 200.
Using inside dimensions for outside work
Flooring measures the inside of a room. Roofing and siding measure the outside. On a small house the difference can be 15% or more, which is more than the entire waste buffer.
Rounding up too early
Round up only after you have summed all areas and added the waste buffer. Rounding up every individual room overstates the total by two to five percent, which on a whole house can add a full box of flooring.
Ignoring waste for diagonal layouts
Diagonal and herringbone installations cut across the plank or tile pattern, so more of each piece is wasted. A 10% buffer that is fine for a straight grid is too small for a diagonal layout. Use 15% for diagonal and 20% for herringbone.
Not measuring twice
Rooms are rarely perfectly rectangular. Measure length and width in at least two spots each and use the larger number. A room that is 12 feet at one end and 12 feet 4 inches at the other is 12 feet 4 inches wide for material purposes.
Residential square footage for listings is defined by ANSI Z765, the American National Standard for Single-Family Residential Buildings. Floor area calculations for building codes follow the International Building Code and the International Residential Code. Land area is measured under the Public Land Survey System in the United States and metric equivalents elsewhere. Unit conversions are standardised by NIST Special Publication 811 and ISO 80000.
A 10 by 10 room is 100 square feet. A 12 by 12 room is 144. A 20 by 20 room is 400. One square meter equals 10.764 square feet. One square yard equals 9 square feet. One acre is 43,560 square feet. For flooring, one box typically covers 20 to 30 square feet. For paint, one gallon covers about 350 to 400 square feet per coat. Add the waste buffer before you round up to whole boxes.
People Also Ask
How do I calculate square footage of a room?
Measure the length and width of the room in feet. Multiply them together. A room 12 feet long and 10 feet wide is 120 square feet. If the room has an alcove or closet, measure those separately and add them. For irregular shapes, split the space into rectangles and add the areas.
How many square feet is a 12 by 12 room?
A 12 by 12 room is 144 square feet. Multiply length by width: 12 times 12 equals 144. This is the size of a standard bedroom that fits a queen bed, two nightstands and a small dresser.
How many square feet is a 20 by 20 room?
A 20 by 20 room is 400 square feet. This is the size of a large living room, an open plan kitchen and dining space, or a double garage.
How many square feet in a square meter?
One square meter equals 10.7639 square feet. One square foot equals 0.09290304 square meters. To convert square meters to square feet, multiply by 10.7639. To go the other way, multiply by 0.0929.
How many square feet in an acre?
One acre equals 43,560 square feet, or about 4,047 square meters. A square acre is about 208.7 feet on every side. A quarter acre is 10,890 square feet, and a half acre is 21,780 square feet.
How do I calculate square footage for an irregular room?
Split the room into shapes you can calculate easily: rectangles, triangles and circles. Measure each shape separately, calculate its area, then add them all together. For a curved bay window, treat the curve as a half circle. For an angled wall, treat the triangle behind it as a triangle with base and height.
How much waste should I add to flooring?
For a straight-lay installation in a rectangular room, add 5 to 10%. For diagonal layouts, add 10 to 15%. For herringbone or complex patterns, add 15 to 20%. The waste covers offcuts, defects, future repairs and dye-lot mismatches.
Should I measure in feet or meters?
It depends on your market. In the United States, flooring, paint, roofing and real estate listings all use square feet. In most other countries, the same materials are sold by the square meter. The calculator above accepts input in feet, inches, meters, centimeters and yards, and outputs both square feet and square meters so you can quote either.
Does the square footage of a house include walls?
No. Residential square footage under ANSI Z765 measures the inside of the exterior walls, not the thickness of the walls themselves. Stairs are counted once, not twice. Garages, basements and unfinished attic space are usually excluded from the main living area figure.
How do I subtract doors and windows from wall square footage?
Measure each door or window as a rectangle and subtract its area from the wall area. A standard interior door is about 21 square feet. A standard window is about 15 square feet. Wall outlets and switches are negligible and usually left in. Built-in cabinets and fireplaces usually are subtracted.
How do I convert square feet to square yards?
Divide square feet by 9. One square yard equals 9 square feet. Carpet in the United States is often sold by the square yard, so a room of 180 square feet needs 20 square yards. Add the waste buffer before converting.
How many square feet does a gallon of paint cover?
One gallon covers 350 to 400 square feet per coat on smooth interior walls. On textured walls, exterior surfaces or porous masonry, coverage drops to 250 to 350 square feet. For a two-coat job, divide the total wall area by the coverage rate and multiply by two. Always round up to the nearest gallon.
Is this calculator free and does it store my data?
Yes and no. Every calculation runs entirely in your browser. Nothing is sent to a server, nothing is stored. Your inputs are not saved anywhere. The only thing remembered is the rating counter, which uses your browser's local storage and never leaves your device.
Related Calculators
References
- ANSI Z765 Standard for Single-Family Residential Buildings, Square Footage Method for Calculating.
- International Code Council, International Building Code and International Residential Code.
- National Institute of Standards and Technology, NIST Special Publication 811, Guide for the Use of the International System of Units.
- International Organization for Standardization, ISO 80000-3 Quantities and Units, Space and Time.
- National Institute of Standards and Technology, NIST Handbook 44, Specifications, Tolerances and Other Technical Requirements for Weighing and Measuring Devices.
Confirm final quantities against the material supplier's coverage chart and add a waste allowance before ordering. Square footage from this calculator is a planning estimate.