Square Footage Calculator finds total area using A = L × W, triangle, circle, or section area inputs, then shows sq ft, cost, conversions, perimeter, acreage, and metric equivalent.
What the Square Footage Calculator Measures
Square footage is the two-dimensional surface area of a flat plane, measured in square feet (sq ft) in the US Customary system or square meters (sq m) in metric. It answers one question: how much flat surface does this space cover?
This sq ft calculator supports four shape modes to match the geometry of the area you are measuring:
▭ Rectangle / Square
A four-sided area with all right angles. Defined by length and width. Covers rooms, slabs, floors, walls, decks, and patios.
▷ Right Triangle
A three-sided shape where the base and height form a 90° corner. Defined by base length and perpendicular height. Covers diagonal wall sections and gabled rooflines.
◯ Circle / Round
A perfectly round area. Defined by diameter. Covers round pads, circular garden beds, round rugs, and column bases.
⊞ Area per Section
For areas where the sq ft per section is already known. Enter the known area and a quantity; the calculator scales the total. Useful for repeated tiles, panels, or pre-measured zones.
The Quantity field multiplies the single-shape area by the number of identical sections. A quantity of 3 means three identical rooms, three identical triangular gable panels, or three identical circular pads — the total area covers all of them together.
Square Footage Formulas Used
Each shape uses a standard geometric formula to calculate the single-section area. The total area and cost are derived from those results.
Multiply length by width. Applies to any rectangular or square floor area, wall panel, or flat slab.
Half of base times height. B and H must be the two sides that meet at the right angle, not the hypotenuse.
Pi times the radius squared. The calculator derives the radius from the entered diameter: r = D ÷ 2.
Cost = Atotal × price per area
Quantity Q scales the single-shape area to the full surface. Cost is computed only when a valid price is entered.
Total edge length around a rectangle — used for trim, baseboard, edging, and fencing estimates.
Sum of both legs plus the calculated hypotenuse. Useful for cutting trim on diagonal sections.
Pi times diameter gives the outer boundary of a circle, reported as boundary length for edging or border material.
How to Use the Calculator
Select US Customary to work in feet and get results in sq ft, sq yd, sq in, and acres. Select Metric to work in meters and get results in sq m, sq cm, sq mm, and hectares. Switching systems resets inputs to sensible defaults and converts all output labels automatically.
Pick the shape that matches the surface you are measuring: rectangle/square, right triangle, circle/round, or area per section. The dimension inputs update to match — for example, the circle mode shows a single Diameter field, while rectangle mode shows both Length and Width.
Type the measured length, width, base, height, diameter, or known area depending on your selected shape. Decimal values are accepted — for example, 12.5 ft or 3.75 m. Measure in the same unit as the selected system. For right triangles, measure only the two sides that meet at the 90° corner.
Enter the number of identical sections. Use 1 for a single room or surface. Use a whole number greater than 1 to cover multiple identical areas — such as 4 equal bedrooms or 6 identical triangular roof panels. The calculator multiplies the single-shape area by this number to produce the total.
If you know the material cost per sq ft (or per sq m in metric mode), enter it to get a Cost Estimation output. Leave it blank or at zero to skip cost output entirely. This field supports flooring, tiling, carpet, paint, sod, gravel, and any other material priced per unit area.
Click Calculate Area to scroll directly to the results. The large hero value shows the total area. Below it, four output cards break down cost, alternate unit conversions, boundary length, and large-scale area context. Results update live as you type.
Example Calculation
This example matches the calculator's default values — a 12 ft by 10 ft rectangular room with one section and a material cost of $2.00 per sq ft.
Input values US Customary · Rectangle
Area calculation
Full output
Understanding the Result Cards
The calculator returns five output areas. Here is what each one shows and when it is most useful.
The main output. The total 2D surface area aggregated across all sections. Shown in sq ft (US) or sq m (metric). This is the number used to order flooring, carpet, tile, paint, sod, gravel, or any coverage-based material.
Shows total estimated material cost and cost per single section, based on the price per area unit entered. Useful for flooring quotes, tiling budgets, carpet estimates, lawn treatment, or any material with a known per-unit-area rate. Hidden when no price is entered.
In US mode: total area expressed in square yards and square inches. Square yards are common for carpet and upholstery; square inches for small tile work or precise cut planning. In metric mode: square centimeters and square millimeters. Also shows area per individual shape for reference.
The outer edge distance — perimeter for rectangles and triangles, circumference for circles. Shows both per-shape and total across all sections. Useful for estimating linear materials: baseboard trim, wall molding, edging, border tile, fencing, garden edging, and retaining wall length. Not applicable in Area per Section mode.
In US mode: total area in acres and equivalent square meters. In metric mode: total area in hectares and equivalent square feet. Useful for landscaping, land assessment, large outdoor areas, and cross-referencing between measurement systems without manual conversion.
When to Use Each Shape Mode
Match the shape mode to the geometry of the surface you are measuring. Using the wrong mode will produce an incorrect area.
| Shape Mode | Required Inputs | Common Applications |
|---|---|---|
| Rectangle / Square | Length, Width | Rooms, hallways, closets, concrete slabs, floor area, wall panels, patios, driveways, decks, raised beds, window glass |
| Right Triangle | Base Length, Height | Triangular gable walls, corner sections, diagonal tile cuts, ramp footprints, triangular garden sections — only when the two measured sides form a right angle |
| Circle / Round | Diameter | Round concrete pads, circular garden beds, round pool footprints, column base coverage, round rugs, circular patio areas, fire pit surrounds |
| Area per Section | Known area per section | Pre-measured sections, repeated tile panels with known size, rooms already calculated elsewhere, combining known sub-areas into a total, material coverage from a spec sheet |
Measurement Notes and Limits
Right triangle mode requires perpendicular sides. The base and height inputs must be the two legs that meet at the 90° corner. Do not enter the hypotenuse as either value — the calculator derives the hypotenuse internally from the two legs.
Boundary length is a linear measure, not an area. Perimeter and circumference are edge distances in feet or meters. They are used for trim, molding, edging, and fencing — not for calculating coverage of surface materials.
Price is optional and must be zero or greater. Leave the price field blank or enter 0 to skip cost output. A negative price will trigger a validation warning and cost results will be suppressed until corrected.
Decimal dimensions are accepted; quantity must be a whole number. You can enter 14.25 ft for a length, but quantity must be a positive integer such as 1, 2, or 5. Fractional quantities are not valid.
This calculator measures flat 2D surface area only. It does not account for surface texture, slope, or elevation. For sloped roofs, curved walls, or irregular polygons, additional measurements outside the scope of this tool are required.
Material orders may require overage. The calculated area reflects exact coverage. Actual material purchases for flooring, tile, carpet, and similar products typically include a waste allowance for cuts, seams, and layout — the appropriate percentage depends on the specific job and material type.
References
- [1] National Institute of Standards and Technology. NIST Special Publication 811: Guide for the Use of the International System of Units (SI). U.S. Department of Commerce. nist.gov/pml/special-publication-811
- [2] National Institute of Standards and Technology. NIST Handbook 44: Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices. U.S. Department of Commerce. nist.gov — HB44
- [3] OpenStax. Prealgebra 2e — Chapter 9: Geometry: Area, Perimeter, and Volume Formulas. Rice University. openstax.org/books/prealgebra-2e