Square Footage Calculator: Rooms, L-Shapes, Irregular Spaces, and Multiple Floors

Square footage drives almost every home project estimate — flooring material quantity, paint needed, HVAC sizing, property taxes, and real estate valuation all start with an accurate area measurement. Getting it right requires knowing which formula to use for each room shape, which areas to include, and which to exclude depending on the purpose of the measurement.

Our  handles rectangular rooms, L-shapes, triangles, circles, and multi-room projects. This guide covers the measurement method for every common scenario.

The basic formula

Area = Length x Width

For a rectangular room, measure the length and width at their longest points, multiply, and you have the square footage. For a 12 x 15 ft bedroom: 12 x 15 = 180 sq ft.

Always measure in feet for square footage. If you measure in inches, divide each dimension by 12 before multiplying.

L-shaped rooms

Divide the L-shape into two rectangles. Measure each and add the areas.

Method A: split into two rectangles

Draw a horizontal line across the L to create two rectangles. Measure each and add.

Example: living room and dining area

Main area: 20 ft x 15 ft = 300 sq ft

Extended alcove: 10 ft x 8 ft = 80 sq ft

Total: 380 sq ft

Method B: large rectangle minus corner

Calculate the full bounding rectangle, then subtract the corner that is not part of the room.

Bounding rectangle: 20 ft x 23 ft = 460 sq ft

Missing corner: 10 ft x 8 ft = 80 sq ft

Area: 460 - 80 = 380 sq ft (same result)

Triangular rooms and areas

Area = (Base x Height) / 2

The height must be perpendicular to the base — measure straight up from the base to the opposite corner.

Example: triangular bay or attic floor section

Base: 12 ft, Height: 9 ft

Area = (12 x 9) / 2 = 54 sq ft

Circular and curved spaces

Area = π x radius²

For a circular room or curved section:

Diameter 14 ft → radius = 7 ft

Area = 3.14159 x 7² = 3.14159 x 49 = 153.9 sq ft

For a semicircle (half circle): divide the full circle area by 2.

What to include and exclude

For flooring calculations

Include all floor area that will receive material. Do not subtract for kitchen islands or cabinets that will sit on the floor — material goes under them. Do subtract for large permanent fixtures like bathtubs and shower pans.

For paint calculations

Calculate wall area: (perimeter x ceiling height) minus door and window openings.

Example: 12 x 15 room, 9 ft ceilings, one door (3 x 7 ft), two windows (3 x 4 ft each):

Perimeter: (12 + 15) x 2 = 54 ft

Wall area: 54 x 9 = 486 sq ft

Subtract: door (21 sq ft) + 2 windows (24 sq ft) = 45 sq ft

Net wall area: 486 - 45 = 441 sq ft

One gallon covers 350-400 sq ft. This room needs approximately 1.1-1.3 gallons per coat.

For real estate and appraisal

The American National Standards Institute (ANSI) standard for measuring residential square footage:

• Include: finished above-grade living space only
• Include: stairways (counted once), interior walls
• Exclude: garages, unfinished areas, basements (even finished basements are typically excluded from "above-grade" square footage, though disclosed separately)
• Exclude: areas with ceiling height below 5 feet (common for attic rooms with sloped ceilings)

Real estate square footage is not always the same as what you would measure for flooring — and it varies by local market convention. Always verify with your appraiser or listing agent which standard is being used.

Multi-room totals

Room	Dimensions	Area
Master bedroom	14 x 16 ft	224 sq ft
Bedroom 2	11 x 12 ft	132 sq ft
Bedroom 3	10 x 11 ft	110 sq ft
Living room	18 x 22 ft	396 sq ft
Kitchen	12 x 15 ft	180 sq ft
Bathrooms (2)	7 x 9 ft each	126 sq ft total
Hallways	Estimated	80 sq ft
Total		1,248 sq ft

Waste factors for flooring materials

When ordering flooring, always add a waste factor to the calculated square footage:

Material	Waste factor	Reason
Carpet	10-15%	Seam placement, room geometry
Hardwood (straight lay)	7-10%	End cuts, defects
Hardwood (diagonal)	12-15%	More angled cuts
Ceramic tile (straight)	10%	Cuts, breakage
Ceramic tile (diagonal)	15%	More cuts
Luxury vinyl plank	7-10%	Cuts, pattern matching

Calculate total area for any combination of room shapes with the .