📐 Square Footage Calculator: Feet, Inches, Any Shape or Room

Use this square footage calculator to find the area of any room, surface, or outdoor space. Enter your dimensions in feet, inches, yards, meters, or centimeters. Get results in square feet, square yards, and square meters instantly.

Whether you are ordering flooring, planning a paint job, estimating tile, or measuring a lot, the right area figure prevents costly material mistakes. This page covers the formula, every common shape, waste factors by material type, and conversion tables.

What Is Square Footage and Why It Matters

Square footage is the total area of a flat surface measured in square feet. It tells you how much space you are working with, whether that is a single room or an entire property.

It comes up in more situations than most people expect:

• Property listings and real estate appraisals
• Building permits and zoning applications
• Flooring, tile, paint, and wallpaper material orders
• HVAC sizing and insulation planning
• Rental pricing and commercial lease negotiations

A wrong measurement does not just affect one line item. If your base area is off by 5%, that error shows up in every material order tied to it. Flooring, drywall, paint, and trim all get shorted.

One thing worth knowing early: gross square footage, net square footage, and livable square footage are not the same number. Contractors, appraisers, and buyers each measure differently depending on what the figure is used for. That distinction is covered in detail in the house measurement section below.

How to Calculate Square Footage: The Basic Formula

The basic formula is straightforward:

Area = Length x Width

Multiply the length of a space by its width, and you get the area in square feet, as long as both measurements are already in feet.

A room that measures 15 ft long by 12 ft wide has an area of 180 sq ft. That number is what you need before ordering flooring, estimating paint, or comparing contractor quotes.

How to Calculate Square Footage in Feet and Inches

Most tape measures show feet and inches, not decimal feet. Before multiplying, convert the inches portion to a decimal.

Divide the inches by 12, then add the result to the whole-foot number.

• 10 ft 6 in becomes 10 + (6/12) = 10.5 ft
• 8 ft 3 in becomes 8 + (3/12) = 8.25 ft

Then multiply the two converted dimensions as normal. The calculator above handles this automatically when you select feet and inches as your input unit.

How to Calculate Square Footage from Inches Only

For small surfaces like countertops, backsplash panels, or tile samples, it is easier to measure everything in inches first.

• Multiply length in inches by width in inches to get square inches.
• Divide by 144 to convert to square feet.

A 36 in by 24 in backsplash section works out to 864 sq in, which equals 6 sq ft.

How to Calculate Square Footage from Meters or Centimeters

If your measurements are in metric units, convert before multiplying, or use the unit selector in the calculator.

• Meters to feet: multiply by 3.28084
• Centimeters to feet: divide by 30.48
• Square meters to square feet: multiply the m2 result by 10.764

Square Footage Formulas for Every Shape

Rooms and surfaces are not always rectangles. Here are the formulas for the shapes that come up most often in home and construction projects.

Rectangle and Square

• Rectangle: Area = Length x Width
• Square: Area = Side x Side

Use these for rooms, driveways, patios, lawns, and wall sections. A square is just a rectangle with all sides equal.

Triangle

Two methods apply depending on what you know:

• Base and height known: Area = Base x Height / 2
• All three sides known (Heron’s formula): s = (a + b + c) / 2, then Area = square root of s(s-a)(s-b)(s-c)

Triangular shapes appear in gable roof ends, corner garden beds, and oddly shaped lots. The calculator supports both methods under the triangle shape option.

Circle

• Area = Pi x Radius squared (3.14159 x r x r)
• If you have the diameter, divide by 2 to get the radius first.

A circular pool with a 10 ft diameter has a radius of 5 ft. Its area = 3.14159 x 25 = 78.54 sq ft.

Trapezoid

• Area = (Base 1 + Base 2) / 2 x Height

Trapezoids appear in angled rooms, irregular lots, and sloped garden beds where one end is wider than the other.

L-Shaped and Irregular Rooms

Split the room into two or more rectangles. Measure each section separately, then add the areas together.

Example: a 20 ft x 10 ft main room plus an 8 ft x 6 ft alcove gives 200 + 48 = 248 sq ft total.

Sketch the layout on paper first, label each section, then measure each one independently. This method works for any shape that can be broken into rectangles, triangles, or a combination of both.

Cylinder Surface Area

• Lateral area = 2 x Pi x Radius x Height

Used for pipe insulation, ductwork, and tank surface coating. Enter the radius and height of the cylinder in the calculator to get the square footage of the curved surface.

How to Calculate Square Footage of a Room

Follow these steps for an accurate room measurement:

1. Measure the length of the room from one interior wall to the opposite interior wall.
2. Measure the width the same way.
3. Multiply length by width to get the area.
4. If the room has an alcove, bay window, or closet, measure those sections separately and add or subtract as needed.
5. Apply a waste factor before ordering any material.

Always measure at floor level. Walls are rarely perfectly parallel, so measure in two or three spots and use the average.

How to Measure Multiple Rooms

For whole-home flooring or painting projects, calculate each room individually, then add all the areas together for the total.

• Use the Multi-Room tab in the calculator to enter each room by name and dimension.
• The tool tracks a running total and applies a single waste factor across all rooms.
• This prevents the rounding errors that build up when you add waste percentages room by room.

Rooms with Angled Walls or Alcoves

Treat any angled or non-rectangular section as a separate shape. A bay window alcove is typically a rectangle or a trapezoid. A room with a diagonal cut corner contains a triangle.

Measure each subsection, calculate its area using the correct formula, then add everything together. No special tool is needed if you decompose the shape correctly.

How to Calculate Square Footage of a House

For residential real estate, appraisers follow the ANSI Z765 standard. Under this standard:

• Only finished, heated, above-grade living area counts toward the reported square footage.
• Garages, unfinished basements, and open porches are excluded from the main figure.
• Each floor level is measured separately, then all floors are added together.
• For a two-story house, measure each floor’s interior footprint and sum both.
• Stairs count on the floor they originate from.

Builders often measure from the outside of exterior walls, which produces a larger number. That figure is not the same as the appraised living area. Both numbers are legitimate but they serve different purposes.

House Square Footage for Appraisal

Appraisers measure finished, above-grade interior space only. Attic space qualifies if it is finished, heated, and accessible by a permanent staircase. Basement area is reported separately from above-grade area, even if it is fully finished.

If you are preparing a home for sale, use the ANSI Z765 method to match what the appraiser will report. Listing a larger number than the appraised figure creates problems during the transaction.

Rentable vs Useable vs Gross Square Footage

This distinction matters on commercial leases and is often skipped by residential measurement guides.

• Useable square footage: the space a tenant actually occupies, measured to the inside face of walls.
• Rentable square footage: useable area plus a proportional share of common areas like lobbies, hallways, and restrooms.
• Gross square footage: the total building area including structural walls, mechanical rooms, and all common spaces.

The difference between useable and rentable is called the load factor, typically 12 to 18 percent on commercial leases. A lease quoted at 8,000 RSF with a 15 percent load factor means the actual carpet area is closer to 6,800 sq ft. Knowing this before signing avoids a common and expensive surprise.

How to Calculate Square Footage of a Roof

Roof area is always larger than the floor footprint because the slope of the roof adds surface area that the flat plan view does not show.

1. Measure the flat footprint of the house: length x width.
2. Determine the roof pitch, expressed as rise over run (for example, 6/12 means 6 inches of rise for every 12 inches of horizontal run).
3. Multiply the flat footprint by the pitch multiplier for that slope.

Common pitch multipliers:

• 4/12 pitch: multiply by 1.054
• 6/12 pitch: multiply by 1.118
• 8/12 pitch: multiply by 1.202
• 12/12 pitch: multiply by 1.414

Roofing materials are ordered by the “square,” which equals 100 sq ft of roof area. Divide your total roof square footage by 100 to get the number of squares needed, then add 10 to 15 percent for waste on hips, valleys, and cuts.

Roof Square Footage by Address

Some online tools pull satellite imagery to estimate roof area from a property address. Accuracy depends on satellite resolution and roof complexity. These estimates work as a starting point for budgeting but should always be verified with physical measurements before ordering materials.

Square Footage for Common Home Projects

Flooring

Measure the total floor area of all rooms to be covered. Add rooms together before applying the waste factor, not after.

Recommended waste by flooring type:

• Hardwood: 5 to 8 percent
• LVP and laminate: 7 to 10 percent
• Ceramic or porcelain tile, straight lay: 10 to 15 percent
• Tile on a diagonal or herringbone pattern: 15 to 20 percent
• Carpet: 10 percent

Round the final material order up to the next full box or bundle. A job that calculates to 437 sq ft needs the next full box above that number, not a partial.

Tile

For floor tile, measure the room area and apply the waste factor above. For wall tile, measure the height and width of each wall section to be tiled, then subtract window and door openings.

For backsplash tile, measure the width and height of the tile field above the counter, then subtract outlet cutouts. Backsplash areas are small, so a 15 percent waste factor is practical for absorbing cuts around outlets and corners.

Paint

Paint covers walls and ceilings, not floors. Wall area is not the same as floor area.

• Wall area = room perimeter x ceiling height
• Subtract approximately 21 sq ft for each standard door opening.
• Subtract approximately 15 sq ft for each standard window.

One gallon of paint covers 350 to 400 sq ft at one coat. For two coats, double the quantity. For rough or porous surfaces, coverage drops to 200 to 300 sq ft per gallon.

Carpet

Carpet is sometimes sold by the square yard. One square yard equals 9 sq ft. Divide your total square footage by 9 to get square yards if the supplier quotes by the yard.

For stairs, measure each tread and each riser separately. A standard stair step has a tread of about 10 inches and a riser of about 7.5 inches. Multiply each step’s combined area by the number of steps, then add to the floor total.

Countertops

Standard kitchen counters are 25 inches deep. Bathroom vanities are typically 22 inches deep. Measure each run of countertop in inches, convert to feet, then multiply by the depth to get square footage.

Add each run together for the total. Most stone fabricators charge by the square foot and include a standard edge profile in that rate.

Drywall

Measure every wall and ceiling surface to be covered. A standard drywall sheet is 4 ft x 8 ft, covering 32 sq ft. Divide the total area by 32 to get the number of sheets, then add 10 to 12 percent for cuts around doors, windows, and outlets.

Siding

Measure each exterior wall face: width x height. Subtract window and door openings from each wall. Add all walls together, then add 10 percent for lap and cut waste. Siding is ordered by the “square,” which equals 100 sq ft, the same convention used in roofing.

Wallpaper

Measure the full room perimeter, multiply by wall height, then subtract large openings. Add 10 to 15 percent for standard patterns and up to 20 percent for large-repeat patterns, since you lose material matching repeats at each seam.

Waste Factor Guide by Material

Ordering without a waste allowance almost always results in a material shortage. Use these figures as starting points and adjust up for complex layouts, diagonal cuts, or heavily patterned materials.

• Hardwood flooring: 5 to 8 percent (straight lay), 10 percent (diagonal)
• LVP and laminate: 7 to 10 percent, 12 percent for diagonal layouts
• Ceramic or porcelain tile: 10 to 15 percent, 15 to 20 percent for diagonal
• Natural stone tile: 15 percent minimum, 20 percent or more for complex cuts
• Carpet: 10 percent
• Drywall: 10 to 12 percent
• Paint: 5 percent for trim cuts on walls, no additional waste needed for field area
• Wallpaper: 10 to 15 percent, more for large pattern repeats
• Exterior siding: 10 percent
• Roofing shingles: 10 to 15 percent, 15 percent or more for hips and valleys

The waste factor field in the calculator lets you enter any percentage. The result panel shows both the net area and the total area to order so you can see exactly how much the waste adds.

Square Footage Unit Conversions

Square Feet to Square Yards

Divide square feet by 9. One square yard equals 9 square feet. Carpet and some older tile products are still priced and sold by the square yard in many markets.

Square Feet to Square Meters

Divide square feet by 10.764. One square meter equals 10.764 sq ft. This conversion comes up on metric material specs and international construction documents.

Square Feet to Acres

Divide square feet by 43,560. One acre equals 43,560 sq ft. A half-acre lot is 21,780 sq ft. This is the conversion to use when comparing lot sizes described in different units.

Square Feet to Linear Feet

Linear feet measure length, not area. To reverse the calculation, divide the square footage by the known width of the material.

Example: 200 sq ft of 5-inch-wide flooring boards requires 200 / (5/12) = 480 linear feet of board.

Square Feet to Cubic Yards

This conversion requires a depth input. Multiply the area in sq ft by the depth in feet, then divide by 27.

Example: a 400 sq ft patio slab at 4 inches (0.333 ft) deep = 400 x 0.333 / 27 = 4.94 cubic yards of concrete.

Price Per Square Foot

Price per sq ft = total cost divided by total square footage. It is the standard unit for comparing contractor bids, valuing properties, and estimating material spend.

Cost Per Square Foot for Flooring

Multiply your total area (including waste) by the material price per sq ft. Add the installation rate per sq ft to get the full installed cost.

Rough ranges as of current market rates:

• LVP flooring installed: $3 to $6 per sq ft
• Hardwood installed: $6 to $12 per sq ft
• Ceramic tile installed: $5 to $10 per sq ft

Price Per Square Foot for Rent

Commercial leases quote rent as an annual rate per sq ft. Divide the annual rent by the total sq ft to get the rate, or multiply the rate by the sq ft to get annual rent.

A 1,000 sq ft office at $24 per sq ft per year costs $2,000 per month.

Price Per Square Foot for a Home

Divide the sale price by the finished living area. A $360,000 home at 1,800 sq ft comes to $200 per sq ft. Comparing this figure to recent neighborhood sales tells you quickly whether a listing is priced at, above, or below the local average.

Common Square Footage Mistakes

These errors appear consistently in home and construction projects. Each one is straightforward to avoid once you know what to watch for.

• Mixing feet and inches without converting: always convert every dimension to decimal feet before multiplying.
• Measuring from exterior walls instead of interior faces: for room area and material orders, measure finished interior face to finished interior face.
• Skipping the waste factor: ordering the exact net area almost always results in running short. Use the waste percentages in the table above.
• Counting the garage or unfinished basement as living area: report finished, heated, above-grade space separately when describing a home’s size.
• Using floor area to estimate wall paint: wall area is perimeter multiplied by ceiling height, minus door and window openings.
• Rounding down to save material cost: always round up to the next full box, bundle, sheet, or square. Ordering a second shipment later costs more than getting it right the first time.
• Scaling from a PDF plan without checking the drawing scale: confirm a known dimension against the stated drawing scale before taking any measurements off a plan.

Frequently Asked Questions

Conclusion

Area measurement is the foundation of almost every home and construction project. Get the number right once and every material order, cost estimate, and contractor comparison that follows stays accurate. Use the square footage calculator at the top of this page for any shape, any unit, and any number of rooms. The waste factor and cost fields are there when you need them. The unit converter tab handles the rest.