The Square Footage Calculator converts measured lengths into area in square feet, square yards, square metres and acres. Ten shapes are covered: rectangle, square, circle, triangle, trapezoid, parallelogram, sector, annulus, rectangle border and circle border. Enter dimensions in feet, inches, yards, centimetres or metres, add openings where they apply, and stack multiple rooms into a single running total.
Calculate square footage by shape
Every plan area reduces to one of ten geometries, and picking the right one removes the need to force an odd room into a rectangle it does not fit. A rectangle is length times width. A circle uses the radius squared.
A trapezoid averages its two parallel sides before multiplying by height. The calculator switches its input fields the moment a different shape is selected.
Match the room or surface to a shape:
- Rectangle or square: bedrooms, garages, most slabs. Length times width, or one side squared.
- Circle: round patios, silo pads, circular planters. Diameter goes in, radius is squared internally.
- Triangle: gable ends, triangular lots. Base and height, or three sides through Heron's formula.
- Trapezoid: cathedral walls, tapered lots. Two parallel sides averaged, times height.
- Parallelogram: skewed additions, angled garages. Base times height, ignoring the slant.
- Sector: a pie-slice cut from a circle, useful for curved deck sections. Radius and angle.
- Annulus: a ring, such as the paved area around a circular pool. Outer and inner diameter.
- Rectangle border or circle border: a walkway or patio strip that wraps a shape's edge, entered as an outer dimension and a border width.
A shed pad, a driveway apron and a living room might all use the plain rectangle mode. A round above-ground pool deck is where the annulus and sector modes earn their place, since a rectangle forced around a curve either falls short or wastes material.
Measure a room in feet and inches
Rooms are rarely built to a whole foot, so the calculator accepts feet and inches on every dimension field rather than forcing a decimal conversion before typing. A tape measure reading of 14 feet 6 inches goes in as 14' 6", and the engine converts it to 14.5 decimal feet internally before multiplying.
Take a bedroom measuring 14' 6" long and 11' 3" wide. Convert each dimension to decimal feet first:
1. Convert the length. 14' 6" = 14 + 6÷12 = 14.5 ft
2. Convert the width. 11' 3" = 11 + 3÷12 = 11.25 ft
3. Multiply. 14.5 ft × 11.25 ft = 163.125 ft²
That comes out to about 163 square feet, close enough to round for flooring but exact for anything priced per square foot. An alcove or a bay window adds a second small rectangle to the same total rather than forcing a single irregular shape; measure the alcove separately and add its area to the room's.
Apply the area formula
Each shape resolves to a short formula, and the calculator runs the exact one behind the scenes so no manual substitution is needed. Rectangles and squares use straight multiplication. Curved and angled shapes route through a radius, an average side, or a triangle solver, but every path ends in the same square-foot output.
Rectangle = Length × Width
Square = Side²
Circle = π × (Diameter ÷ 2)²
Trapezoid = ½ × (Side A + Side B) × Height
Parallelogram = Base × Height
Sector = ½ × Radius² × Angle (radians)A round patio 10 ft across works out as π × (10 ÷ 2)² = π × 25 = 78.54 ft². A triangular gable end with an 18 ft base and a 6 ft rise to the ridge is ½ × 18 × 6 = 54 ft². For a triangle known only by its three side lengths, Heron's formula finds the semi-perimeter first, then the square root of four half-perimeter terms multiplied together. Enter the three sides and the calculator returns the area without the reader needing to remember the derivation.
Calculate a wall minus its openings
A wall's paintable or buildable area is its full rectangle minus every door and window cut into it. The calculator subtracts each opening by its own measured width and height rather than a flat assumption, since a 30-inch door and a 36-inch door are not the same deduction.
Net wall area = (Wall length × Wall height) − Σ (Opening width × Opening height)A wall measuring 20 ft long and 9 ft high has a gross area of 180 ft². One door at 3 ft wide by 6 ft 8 in tall removes 3 × 6.667 = 20 ft². The net area is 180 − 20 = 160 ft². Add a second opening, a window, and its own width times height comes off the same running total. This net figure is the one to hand a flooring or drywall estimator; the gross figure overstates material by exactly the area of every opening in the wall.
Add multiple rooms into one total
A whole floor or a whole house is the sum of its rooms, and the calculator keeps a running list rather than making the reader add subtotals by hand. Each row is named, so the breakdown stays legible instead of collapsing into a single unexplained number.
A three-room total might read: Living room 240 ft², Kitchen 120 ft², Total 360 ft². Adding a third room, a 14' 6" × 11' 3" bedroom at 163.125 ft², brings the running total to 523.125 ft². Every row stays visible in the result panel, so a client asking "where did that number come from" gets an itemised answer instead of a single figure with no working behind it.
Convert square feet to other units
Square feet is the working unit for most US construction, but material and lot listings often use a different one, and the conversion factor changes for each target unit. There are 9 square feet in a square yard, 43,560 square feet in an acre, and 144 square inches in a square foot.
| Convert from ft² | Factor | Example |
|---|---|---|
| To square yards | Divide by 9 | 360 ft² ÷ 9 = 40 yd² |
| To acres | Divide by 43,560 | 3,000 ft² ÷ 43,560 = 0.069 acres |
| To square metres | Multiply by 0.0929 | 360 ft² × 0.0929 = 33.4 m² |
| To square inches | Multiply by 144 | 10 ft² × 144 = 1,440 in² |
A 3,000 ft² house sits on about 0.069 acres of footprint, a figure worth separating from lot size, which is almost always larger than the structure built on it. Square yards matter most for flooring and carpet, which is frequently priced and sold by the yard rather than the foot.
Estimate material cost per square foot
Material cost scales directly with area once a price per square foot is known, and the calculator multiplies the two together along with a quantity field for multiple identical rooms or runs. The formula stays simple enough to check by hand.
Cost = Area (in selected unit) × Price per unit × QuantityFlooring quoted at $4.50 per square foot across the 360 ft² living room and kitchen total comes to 360 × 4.50 = $1,620 for material alone, before labour. Installers typically add 5 to 10 percent for cuts, a figure not included here and worth adding before ordering.
Measure irregular and L-shaped rooms
An L-shaped room, a bumped-out closet, or a room with a fireplace cut into one wall does not fit a single rectangle, but every one of them can be split into shapes that do. Draw one line across the irregular outline, measure each resulting piece, and add the pieces together.
An L-shaped living room can be split into a large rectangle 20 ft × 15 ft (300 ft²) and a smaller rectangle 5 ft × 6 ft (30 ft²) that fills the leg of the L, giving 330 ft² total. A room with a closet notched out of one corner does the reverse: measure the full rectangle, then subtract the notch's own rectangle rather than trying to trace the remaining outline directly.
Curved bay windows and rounded corners can be approximated with a rectangle at the curve's average width, or handled exactly with the sector and circle-border modes above. The approximation error is usually smaller than the rounding already built into a tape measurement.
Frequently asked questions
How do I calculate square footage of a house?
Add the finished, heated floor area of every level using exterior wall dimensions, following the same convention appraisers use under ANSI Z765. Unfinished space such as an unheated porch or a garage is measured and reported separately, not folded into the main total. A two-storey house with 1,200 ft² on each level has 2,400 ft² of gross living area.
Does square footage include the garage?
No, not in standard residential reporting. A garage is unfinished, unconditioned space and is listed separately from gross living area, even when it is attached to the house. The same rule applies to unfinished basements: below-grade space is reported on its own line rather than combined with above-grade square footage.
How do I find square footage of an odd shape?
Split the shape into rectangles, triangles or the other shapes the calculator supports, measure each piece, and add the areas together. A shape with a straight cut-out, such as a notch or an alcove, is measured as the full outer shape minus the cut-out's own area rather than traced as one continuous irregular outline.
How many square feet are in a square yard?
Nine. A square yard is 3 ft by 3 ft, and 3 × 3 = 9. Flooring and carpet are commonly priced per square yard, so dividing a room's square footage by 9 converts the area into the unit the quote is likely written in.
How do I convert square feet to acres?
Divide the square footage by 43,560, the number of square feet in one acre. A 10,000 ft² lot is 10,000 ÷ 43,560 = 0.23 acres. This conversion applies to land area; it is not used for the floor area of a house, which stays in square feet or is converted to square metres instead.
Does ceiling height change square footage?
No. Square footage is a plan-view measurement of the floor, taken from directly above, and it does not depend on how tall the room is. Ceiling height matters for volume, paint area and HVAC sizing, but two rooms with identical floor dimensions have identical square footage regardless of whether one has an 8 ft ceiling and the other a vaulted 14 ft one.
What is the difference between square footage and square feet?
None. Square footage is the general term for an amount of area measured in square feet; the two are used interchangeably in construction and real estate. "The house has 2,400 square feet" and "the house has 2,400 ft² of square footage" describe the same figure.
How do I measure square footage for a triangular lot?
Use the base-and-height triangle mode if a perpendicular height is known, or enter all three boundary lengths and let Heron's formula solve it. A triangular lot with sides of 120 ft, 150 ft and 180 ft has a semi-perimeter of 225 ft, giving an area of roughly 8,973 ft² once the four terms under the square root are multiplied out.
Is a laser measure more accurate than a tape measure for this calculator?
A laser measure typically reads within an eighth of an inch over a normal room span, close to a careful tape reading. The larger error source is usually a wall that is not straight or square, not the tool itself.
Why does my flooring quote need more square footage than the room measures?
Flooring installers add a waste allowance, typically 5 to 10 percent, for cuts and material that does not divide evenly across the room. A 300 ft² room at 10 percent waste needs 330 ft² of material, and diagonal layouts push that allowance higher.
Summary
The Square Footage Calculator turns measured dimensions into area across ten shapes, from a plain rectangle to a border wrapped around a circle. Feet-and-inches input avoids a manual decimal conversion, wall modes subtract measured openings rather than a flat guess, and a multi-room accumulator adds named rows into one total.
Square feet converts to square yards by dividing by 9, to acres by dividing by 43,560, and to square metres by multiplying by 0.0929. Split any irregular room into shapes the calculator already handles, add the pieces, and the total holds up to the same scrutiny as a single rectangle.