Area Calculator

Square footage, multi-shape rooms, paint & wallpaper estimators

Calculate area for any shape or room

Units
Inputs
Base times height divided by 2 works for any triangle as long as the height is the perpendicular distance from the base to the opposite vertex.
L-shape auto-decomposes into two rectangles. Enter the long side, the short rectangle width, the offset, and the depth.
Add as many rooms as needed. Each room has its own length, width, wall height, doors, and windows.
Results
Floor Area
0sq ft
Wall Area (subtracts openings)
0sq ft
Square Meters
0m²
Total Surface (Floor + Wall)
0sq ft
8-Unit Conversion
Converted floor area, one row per unit you entered
UnitFloor Area
Square Feet0
Square Meters0
Square Yards0
Square Inches0
Square Kilometers0
Square Miles0
Acres0
Hectares0
Shape Preview

Area Calculator: 6 Shapes and Square Footage

This area calculator works out the area of a rectangle or square, a triangle, a circle, a trapezoid, an L-shaped room and a multi-room floor plan, in feet and inches or in metric, and it turns that area into the numbers a US project needs: square feet for flooring, square yards for carpet, gallons of paint for the walls and rolls of wallpaper. A 12 ft by 10 ft room is 120 square feet; a 10 ft 6 in by 9 ft 4 in room is 98 square feet, not 90. Nothing is uploaded and nothing is stored - the calculation happens in your browser.

Area formulas for the six shapes this calculator supports, with a worked example in feet
ShapeFormulaWorked example
Rectangle / squareLength x width12 ft x 10 ft = 120 sq ft
TriangleBase x height / 220 ft x 10 ft = 100 sq ft
Circlepi x radius squared6 ft radius = 113.1 sq ft
Trapezoid(a + b) / 2 x height(20 ft + 10 ft) / 2 x 8 ft = 120 sq ft
L-shapeTwo rectangles minus the overlap20 ft x 16 ft with an 8 ft x 6 ft notch = 272 sq ft
Multi-roomEvery room added together120 sq ft + 96 sq ft = 216 sq ft

How This Area Calculator Works

Pick a shape mode and enter its dimensions. The calculator applies the standard area formula (length times width for a rectangle, base times height divided by two for a triangle, pi times r squared for a circle, the trapezoid formula (a plus b) divided by two times h, or the auto-decomposition for an L-shape into two rectangles minus the overlap). For wall projects set the wall height above zero and the calculator multiplies the perimeter by the height, then subtracts the standard area of every door (about 21 square feet) and window (about 12 to 15 square feet).

When you add the material estimators the calculator also outputs paint gallons from the wall area divided by surface coverage with the chosen number of coats, wallpaper rolls from the wall area plus pattern repeat waste, and carpet square yards from the floor area plus 10 percent waste. Toggle imperial and metric at any time and every input converts; toggle the 8-unit conversion table to see the floor area in square feet, square meters, square yards, square inches, square kilometers, square miles, acres, and hectares at once.

Why This Beats Asking an AI Chatbot

AI chatbots get the basic rectangle wrong when feet and inches are mixed (10 ft 6 in by 9 ft 4 in should be 98 square feet, not 90), cannot decompose an L-shape into two rectangles and subtract the overlap, do not subtract doors and windows from wall area before computing paint, do not convert between square feet and square meters reliably (the conversion factor is 0.092903, not 0.093 or 10.764), and cannot estimate paint gallons or wallpaper rolls from area. They give a number that feels right but is off by 5 to 30 percent on real projects.

This tool uses the standard area math, auto-decomposes L-shapes, subtracts your openings from wall area, outputs paint gallons and wallpaper rolls in one click, and converts to 8 different unit systems simultaneously. You can save the project to localStorage so it reloads when you come back, copy the result as a plain-text shopping list, and print it to take to the paint or flooring store.

Square Footage for Real Estate and Floor Plans

To get the square footage of a property from a floor plan, measure the length and width of every room in feet, multiply the two numbers, and add the rooms together. An apartment with a living room of 12 ft x 10 ft (120 sq ft), a bedroom of 10 ft x 12 ft (120 sq ft) and a kitchen of 8 ft x 9 ft (72 sq ft) has 312 sq ft of room area before the hallway, the closets or the footprint of the walls are counted.

How to read a floor plan for square footage

Use the written dimension lines on the plan rather than the scale bar: a plan drawn at 1/4 inch = 1 foot still needs the printed numbers, and it is the interior dimension that gives the usable square footage. Measure to the finished face of the wall rather than to the stud, and treat an L-shaped room as two rectangles with the overlap subtracted - a 20 ft x 16 ft living room with an 8 ft x 6 ft notch is 272 sq ft, not 320.

How much flooring and paint to buy

Add 10 percent for waste on a straight layout and 15 percent on a diagonal or herringbone pattern, so 500 sq ft of oak needs 550 to 575 sq ft of material. Carpet is sold by the square yard: 500 sq ft is 55.6 sq yd, and with 10 percent waste you need to buy 61 sq yd. For walls, one gallon of latex covers about 350 sq ft of wall area in a single coat, so a room with 480 sq ft of wall area needs two gallons for one coat or four for two coats - and the wall area is the perimeter times the height, minus the area of the doors and windows. The tile calculator covers the same ground for tile and stone, and the paint calculator works out gallons per coat for a wall area you already have.

Frequently Asked Questions

How do I calculate the square footage of a room?

Measure the length and width of the room in feet using a tape measure, then multiply length by width. A 12 foot by 10 foot room is 120 square feet. For L-shaped rooms split the room into two rectangles, compute each area separately, and add them. The area calculator above handles rectangles, triangles, circles, trapezoids and L-shapes in one click.

How do I find the area of an L-shaped room?

Split the L into two rectangles. Measure the full length of the longest side, then the width of the shorter rectangle and the width of the longer rectangle. Compute area as (long_length times long_width) plus (short_length times short_width). For a more irregular shape add more rooms using the multi-room mode and let the calculator sum them.

How do I convert square feet to square meters?

One square foot equals 0.092903 square meters. Multiply your square foot area by 0.092903 to get square meters, or multiply square meters by 10.7639 to get square feet. The area calculator handles all conversions automatically when you toggle the unit switch at the top.

How do I calculate wall area for paint?

Measure the perimeter of the room (length plus width times 2) and multiply by the wall height in feet. Then subtract the area of every door (typically 21 sq ft) and window (typically 12 to 15 sq ft). One gallon of paint covers about 350 square feet of smooth drywall with one coat, or 175 square feet for two coats over primer.

How many square feet is a 10 by 10 room?

A 10 foot by 10 foot room is 100 square feet. The same room in square meters is 9.29, in square yards is 11.11, and in acres is 0.0023. The area calculator above outputs all four units in one click when you toggle imperial or metric.

Can AI chatbots calculate room area correctly?

AI text models get the basic rectangle wrong when feet and inches are mixed (10 ft 6 in times 9 ft 4 in should be 98 sq ft, not 90), cannot decompose an L-shape into two rectangles, do not subtract doors and windows from wall area, do not convert between square feet and square meters reliably, and cannot estimate paint gallons or wallpaper rolls from area. They give a number that feels right but is off by 5 to 30 percent on real projects.

How many acres are in a square mile?

One square mile equals 640 acres, or 2.59 square kilometers, or 27,878,400 square feet. The area calculator handles every conversion above including acres, hectares, square miles, square kilometers, square yards and square meters in one click when you toggle units or enter the value in the converter panel.

Does this work in metric?

Yes. Toggle the unit switch at the top to Metric and every input switches to meters and centimeters, area switches to square meters, paint switches to liters, and cost switches to the local currency. The math is the same; only the units and product sizes change. The conversion panel below the rooms section accepts any input and outputs all 8 unit systems in one row.

Is my project data private?

Yes. Everything runs in your browser using JavaScript. No room dimensions, area values, or costs are sent to any server. Close the tab and your last project is gone. The only data persisted is the last project in localStorage so the form reloads when you come back. There is no account, no email capture, no analytics tied to your project.

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