Square Footage Calculator

About Square Footage Calculator

What Is Square Footage?

Square footage is the measure of a two-dimensional area expressed in square feet, where one square foot equals a square 12 inches on each side (144 square inches). It is the standard unit for describing room size, floor plans, and property size in the US, UK, and Canada. For a rectangular room, square footage is simply length times width in feet. For non-rectangular spaces, you break the area into simpler shapes (rectangles, triangles, circles) and add the individual areas together. According to the American National Standards Institute (ANSI Z765-2021), a room counts toward a home's "finished square footage" only if it is heated, has a ceiling of at least 7 feet, and is accessible from the main living area - basements and garages typically do not count in US real estate listings.

Area Formulas by Shape

Shape	Formula	Example
Rectangle / square	Length x Width	12 ft x 10 ft = 120 sq ft
Circle	pi x r²	Radius 5 ft: 3.14159 x 25 = 78.54 sq ft
Triangle	(Base x Height) / 2	8 ft base x 6 ft height: 48 / 2 = 24 sq ft
L-shape	(L1 x W1) + (L2 x W2)	Split into two rectangles and add their areas

Area Unit Conversions

From	To	Multiply By
1 square foot	Square metres	0.0929
1 square metre	Square feet	10.764
1 square foot	Square yards	0.1111 (1/9)
1 square yard	Square feet	9
1 acre	Square feet	43,560
1 hectare	Square metres	10,000

Typical Room Sizes

Use these as sanity checks when measuring. If your calculation is way outside these ranges, double-check your measurements:

Room	Typical Size Range	Square Footage
Small bedroom	9 x 10 to 10 x 12	90-120 sq ft
Standard bedroom	11 x 12 to 12 x 14	132-168 sq ft
Master bedroom	14 x 16 to 16 x 20	224-320 sq ft
Living room	12 x 16 to 16 x 20	192-320 sq ft
Kitchen	10 x 12 to 14 x 16	120-224 sq ft
Bathroom	5 x 8 to 8 x 10	40-80 sq ft
Garage (single car)	12 x 20	~240 sq ft
Garage (double car)	20 x 22	~440 sq ft
Studio apartment	-	300-600 sq ft total
Average UK home	-	~818 sq ft (76 sq m) per English Housing Survey
New UK build (avg)	-	~721 sq ft (67 sq m)
Average new US single-family home (2024)	-	~2,404 sq ft (223 sq m) per US Census

Why UK and US Homes Differ So Much

The average new US single-family home sold in 2024 was about 2,404 sq ft according to the US Census Bureau Characteristics of New Housing report, while the average English home sits at roughly 818 sq ft per the English Housing Survey. That is nearly a 3x gap, driven by lot sizes, zoning, building codes, and long-standing housing policy. UK homes are among the smallest in Europe, with some Victorian terraces under 500 sq ft still classed as two-bedroom. US new-home sizes peaked at 2,724 sq ft in 2015 and have trended down about 11% over the last decade as buyers push back on affordability. When comparing listings across countries, always check whether the figure includes garages, basements, or outdoor space - definitions vary.

How to Measure Rooms

Step	Instructions
1. Use a tape measure	Measure along the floor at the base of the walls - this is the most accurate point
2. Measure length and width	Measure the longest and widest walls of each section
3. Record in feet and inches	Example: 12 ft 6 in = 12.5 feet. Convert inches by dividing by 12
4. Handle irregular shapes	Split into rectangles, triangles, or circles and add the areas
5. Subtract obstacles if needed	Columns, built-in cabinets, or permanent fixtures that reduce usable area

Common Uses for Square Footage

Purpose	What You Need Area For	Related Tool
Paint estimate	Wall area determines gallons needed	Paint calculator
Flooring purchase	Floor area determines tile, hardwood, or carpet quantity	Tile calculator
HVAC sizing	Room area determines BTU requirements	BTU calculator
Concrete slab	Area x depth = volume needed	Concrete calculator
Mulch / gravel	Area x depth = cubic yards to order	Mulch calculator
Real estate listing	Total living area for property listing	-
Carpet purchase	Area in square yards (divide sq ft by 9)	-
Rental pricing	Price per square foot comparison	-

Handling Irregular Rooms

Most real rooms are not perfect rectangles. Here is how to measure common irregular shapes:

Room Shape	How to Measure
L-shaped room	Split into two rectangles, measure each, and add areas together
Room with a bay window	Measure the main rectangle plus the bay window area (triangle or trapezoid)
Room with a closet alcove	Measure the main room and the closet separately, add if needed
Round / curved wall	Approximate with a rectangle and add or subtract the curved portion
Open plan (multiple areas)	Break into separate rectangular zones and add them all

Price Per Square Foot

Square footage is the standard unit for comparing property prices, renovation costs, and flooring prices. To find price per square foot, divide the total cost by the total square footage. For example, a $300,000 home with 2,000 sq ft costs $150 per square foot. US national data from the National Association of Home Builders shows new single-family construction cost around $164 per sq ft in 2024, though that ranges from roughly $130 in parts of the Midwest to over $300 in coastal metros. In the UK, the Office for National Statistics average price per square metre was around £3,500 in 2024 (roughly £325 per sq ft), with Greater London two to three times that.

Worked Example: Measuring an L-Shaped Living Room

Say you have a living room shaped like an L. The main rectangle is 16 ft by 14 ft, and the smaller arm of the L is 8 ft by 6 ft.

• Main section: 16 x 14 = 224 sq ft
• Extension: 8 x 6 = 48 sq ft
• Total: 224 + 48 = 272 sq ft (about 25.3 sq m)

For flooring, always order an extra 10% to allow for cuts, waste, and pattern matching, so you would order enough material for roughly 300 sq ft. For paint, the same room with 9 ft ceilings has roughly (16+14+16+14) x 9 = 540 sq ft of wall area minus doors and windows, so two coats would need about 2.5-3 gallons based on 350 sq ft coverage per gallon from Sherwin-Williams guidance.

Common Mistakes When Calculating Square Footage

• Measuring in inches without converting. A 12 ft 6 in wall is 12.5 ft, not 12.6 ft. Divide inches by 12, not by 10.
• Counting rooms twice. When summing rooms, make sure the areas do not overlap (for example, if you already measured a bay window as part of the living room, do not add it again).
• Forgetting ceiling height for paint. Floor area does not equal wall area. Wall area = perimeter x ceiling height, minus doors and windows.
• Ignoring room sloping or vaulted ceilings. For attic conversions, standards often count only floor area where the ceiling is at least 5 feet high (the "half-height rule" in the UK RICS Code of Measuring Practice).
• Measuring wall-to-wall without accounting for built-ins. If you are buying flooring, exclude permanent cabinets, kitchen islands, and hearths that will not be covered.

Tips for Accurate Measurement

A 25 ft locking tape measure handles most rooms. Laser distance measures (Bosch GLM, Leica Disto) are accurate to +/- 1/16 inch and speed up multi-room surveys. Measure at floor level, not at hip height, and always take a second measurement at the opposite end of the wall to catch rooms that are not quite square - older homes are rarely exactly rectangular. Record numbers on paper with a rough floor plan rather than trying to remember them. When in doubt, round down slightly for flooring (you will always have offcuts) and round up slightly for paint (a half-empty can is better than a half-painted wall).

For volume calculations involving depth, the cubic yards calculator takes area measurements and multiplies by depth - useful for concrete slabs, gravel beds, and mulch. If you are working out wall area rather than floor area, the general area calculator supports extra shapes. All calculations run in your browser with no data stored.

Sources

• US Census Bureau - Characteristics of New Housing 2024
• GOV.UK - English Housing Survey, Size of English Homes
• NAHB - Cost of Constructing a Home
• RICS Code of Measuring Practice (6th ed.)
• ANSI Z765 - Square Footage Measurement Standard
• Office for National Statistics - UK Housing Statistics