What is the formula for square footage of a circle or triangle?

Circle: pi x radius squared. A 10 ft diameter circle has a 5 ft radius, so pi x 25 = 78.54 sq ft. Triangle: one-half x base x height. A triangle with a 12 ft base and 10 ft height is 0.5 x 12 x 10 = 60 sq ft.

Should I include closets and hallways in a room measurement?

For material ordering, measure each space that will receive the material and add them: closets and hallways count if they get the same flooring. For official living-area figures used in real estate, standards differ, so a DIY measurement should not be treated as an official reported figure.

Square Footage Calculator

Measure rooms in feet, meters, or inches. Add as many rooms as you need, see a running total, and get conversions plus material estimates.

Total square footage

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Quick Examples

What Is Square Footage?

Square footage is the two-dimensional area of a surface expressed in square feet — the area of a 1 ft by 1 ft square, equal to 144 square inches or 0.0929 square meters. It is the base unit for flooring orders, paint quantities, carpet yardage, tile counts, roofing, and real estate pricing per square foot.

Getting the number right — then adding the correct waste allowance — is the difference between ordering once and making a second trip to the store.

The Square Footage Formula

For any rectangle, the formula is simply length times width — in any unit, as long as both measurements match:

Square footage = Length (ft) x Width (ft)

The same formula works in any unit: meters times meters gives square meters, inches times inches gives square inches.

Worked examples

Bedroom: 12 ft x 15 ft = 180 sq ft.
Metric room: 4 m x 5 m = 20 m² = 20 x 10.7639 = 215.28 sq ft.

How to Measure a Room Accurately

Sketch first. Draw the room from overhead, marking doorways, closets, and bump-outs.
Measure wall to wall. Record the longest dimension as the length, the other as the width.
Convert extra inches. Divide extra inches by 12 for decimal feet (12 ft 6 in = 12.5 ft).
Multiply length by width. This is the room's square footage.
Add a waste allowance if the measurement will be used to buy materials.

Feet and Inches: The Most Common Mistake

Because there are 12 inches in a foot, convert inches by dividing by 12: 6 inches = 0.5 ft (not 0.6 ft), 9 inches = 0.75 ft, 3 inches = 0.25 ft (not 0.3 ft).

Worked example: 12 ft 6 in by 10 ft 9 in = 12.5 x 10.75 = 134.375 sq ft. Treating 6 in as 0.6 ft is one of the easiest and costliest mistakes — always divide inches by 12.

Multiple Rooms: Adding Areas Together

For flooring, paint, or whole-house estimates, calculate each room separately and add the results — never multiply a home's longest overall dimensions unless the building is a perfect rectangle. Example for three rooms:

Living room: 15 x 12 = 180 sq ft; bedroom: 12 x 10 = 120 sq ft; hallway: 12 x 4 = 48 sq ft
Total: 180 + 120 + 48 = 348 sq ft; with 10% waste: 348 x 1.10 = 382.8 sq ft to order

The calculator above adds unlimited rooms and keeps a running total automatically.

Irregular and L-Shaped Rooms

Split any irregular space into rectangles, calculate each piece, and add the results. For an L-shape, either split it into two rectangles or calculate the large outer rectangle and subtract the missing corner: outer 15 x 12 ft = 180 sq ft minus a 5 x 4 ft cutout = 20 sq ft gives 160 sq ft.

Other shapes

Shape	Formula	Example
Triangle	1/2 x base x height	1/2 x 12 x 10 = 60 sq ft
Circle	pi x radius²	pi x 5² = 78.54 sq ft
Trapezoid	1/2 x (a + b) x height	1/2 x (10 + 14) x 8 = 96 sq ft

For a triangle, the height must be perpendicular to the base — a sloping side is not necessarily the height. For a circle, the radius is half the diameter.

Wall Square Footage for Paint

Wall area matters for paint, wallpaper, and drywall estimates. For all four walls of a rectangular room:

Wall area = 2 x (Length + Width) x Wall height

Example: a 12 x 10 ft room with 8 ft walls has a 44 ft perimeter, giving 44 x 8 = 352 sq ft gross. Subtract one 3 x 6.67 ft door (20.01 sq ft) and two 3 x 4 ft windows (24 sq ft): 352 - 20.01 - 24 = 307.99 sq ft net paintable area.

Unit Conversions

From	To	Multiply by
Square feet	Square inches	x 144
Square feet	Square yards	/ 9
Square feet	Square meters	x 0.092903
Square feet	Acres	/ 43,560
Square yards	Square feet	x 9
Square meters	Square feet	x 10.7639
Acres	Square feet	x 43,560

Carpet is priced per square yard, commercial drawings use square meters, and lot sizes use acres. A 180 sq ft room is 20 square yards, 16.72 square meters, and 0.0041 acres.

Paint and Flooring Estimator

Raw square footage is the starting point; the number you buy adds a waste factor per material.

Paint coverage

One gallon covers about 350 to 400 sq ft per coat on smooth walls; two coats (a color change) give 175-200 sq ft per gallon effective. Always round up to the next whole gallon — that rounding is your built-in waste buffer, so do not add a separate percentage for paint.

Waste allowance by material

Material	Simple layout	Complex / patterned
Vinyl / laminate	5-10% extra	10-15% extra
Hardwood	7-10% extra	15% extra (diagonal)
Ceramic / porcelain tile	10% extra	15% extra (diagonal)
Carpet	10% extra	+10% for pattern match
Paint	0% (gallons round up)	0%

The calculator above applies your chosen waste percentage to the total and estimates paint gallons from your coverage figure in one pass.

Common Square Footage Mistakes

Inches as decimal feet: 6 in = 0.5 ft, not 0.6 ft. Divide inches by 12.
One big rectangle for an irregular space: section it into simple shapes instead.
Skipping the waste allowance: cuts and pattern matching always consume extra material.
Measuring furniture-to-furniture: measure wall to wall for the area to cover.
Using DIY numbers as official figures: real-estate living area follows specific standards.

Frequently Asked Questions

How do I calculate the square footage of a room?

Measure length and width in feet, wall to wall, then multiply: square footage = length x width. A 12 x 15 ft room is 180 sq ft. Add each room's area for a whole-house total.

How do you convert feet and inches to square feet?

Divide extra inches by 12 to get decimal feet, then multiply. 12 ft 6 in by 10 ft 9 in = 12.5 x 10.75 = 134.375 sq ft. Never treat inches as decimal feet: 6 in is 0.5 ft, not 0.6 ft.

How many square feet are in an acre?

One acre equals 43,560 square feet. Divide square feet by 43,560 to get acres. A 10,000 sq ft lot is about 0.23 acres.

How do I calculate square footage for an L-shaped room?

Split the L into two rectangles and add their areas, or calculate the outer rectangle and subtract the missing corner. Example: 15 x 12 ft outer (180 sq ft) minus a 5 x 4 ft cutout (20 sq ft) = 160 sq ft.

How much extra material should I add for waste?

Add 5-15% depending on material: 5-10% for simple vinyl/laminate, 10-15% for tile and complex layouts, 10% for carpet. Example: 348 sq ft with 10% waste = 382.8 sq ft to order.

How many gallons of paint do I need?

One gallon covers 350-400 sq ft per coat; two coats give 175-200 sq ft per gallon effective. Compute wall area as perimeter x height, subtract doors and windows, divide by coverage, and round up to the next gallon.

How do I calculate wall square footage for paint?

Wall area = 2 x (length + width) x wall height. A 12 x 10 ft room with 8 ft walls = 352 sq ft gross. Subtract one door (about 21 sq ft) and two windows (about 24 sq ft) for roughly 308 sq ft net.

How do I convert square feet to square meters?

Multiply square feet by 0.092903. A 180 sq ft room = 16.72 square meters. To convert back, multiply square meters by 10.7639.

What is the formula for a circle or triangle?

Circle: pi x radius squared (10 ft diameter = pi x 25 = 78.54 sq ft). Triangle: one-half x base x height (12 ft base, 10 ft height = 60 sq ft).

Related Calculators

These tools extend area measurement for projects and geometry:

Area Calculator: areas of circles, triangles, trapezoids, and more shapes.
Perimeter Calculator: perimeters for fencing, trim, and edging.
Length Converter: convert feet, inches, yards, and meters before measuring.
Unit Converter: convert between all common measurement units.
Volume Calculator: from floor area to concrete, soil, and fill volumes.

Conclusion

Square footage is length times width — 12 x 15 ft gives 180 sq ft — and every larger estimate builds on that one multiplication. Measure wall to wall, convert inches by dividing by 12, section irregular rooms into simple shapes, and add a 5 to 15 percent waste allowance matched to your material. For paint, divide net wall area by 350-400 sq ft per gallon and round up.

Use the calculator above to add unlimited rooms with a running total, convert to square meters, square yards, and acres, and get waste-adjusted material and paint estimates.