The Square Footage Calculator estimates the square footage of a lot, house, or other surfaces in several common shapes. If the surface is complex in shape, it may be possible to section the surface into simple shapes and add their square footages together. Enter a quantity to multiply the area, and an optional price per square unit to estimate the cost.
The square footage calculator works out the area of a lot, house, room, wall, garden, or any other surface and returns the answer in square feet — plus acres, square meters, square yards, and every other common unit. It covers nine shapes, so you are not limited to simple rectangles: circles, rings, borders, triangles, trapezoids, sectors, and parallelograms are all included. Each calculator also accepts a quantity, so you can multiply identical areas in one step, and an optional price per square unit that instantly turns your measurement into a cost estimate for flooring, turf, paint, tile, or land.
Square footage is the language of real estate, construction, and home improvement in the United States. It determines what a house is worth, how much material a job needs, and what a contractor will charge. Measuring it correctly is one of the highest-leverage things you can do before starting any project — a 10% error on a flooring order can mean hundreds of dollars wasted or a second trip to the store mid-installation.
Square footage is a measurement of area expressed in square feet. One square foot is the area of a square measuring one foot on each side. Because area is a two-dimensional quantity, it scales with the square of length: double the dimensions of a room and its floor area quadruples. That relationship is also why unit conversions carry surprisingly large factors — there are 144 square inches in a square foot and 9 square feet in a square yard, not 12 and 3.
The abbreviations you will see include ft², sq ft, and SF. In countries using the metric system the equivalent measure is the square meter (m²), where one square meter equals about 10.764 square feet. This calculator lets you measure in whichever unit is convenient and always reports the result in square feet alongside a full conversion table.
Pick the calculator that matches your shape, enter the dimensions, and click Calculate. A few things make it more powerful than a simple length-times-width formula:
The workhorse of square footage. Area = length × width. Most rooms, walls, lots, sheets of material, and building footprints are rectangles. A square is simply a rectangle with equal sides.
Calculates the area of a frame or band running inside the edge of a rectangle: Area = (l × w) − (l − 2b) × (w − 2b), where b is the border width. This is exactly what you need for a walkway around a patio, a decorative tile border around a floor, a mulch strip around a bed, or a mat around a picture. Note that the border is taken from all four sides, which is why the border width is subtracted twice from each dimension.
Enter the diameter — the full distance across the circle — and the calculator finds Area = π × (d/2)². Diameter is used here rather than radius because it is what you actually measure with a tape across a round patio, pool, or table.
A ring (or annulus) is the band between two concentric circles: Area = π × [(d/2)² − (d/2 − b)²]. Enter the outer diameter and the border width. Use it for a circular walkway around a fountain, the border of a round rug, or a ring of planting around a tree.
When you know all three sides but no angles or height, Heron's formula gives the area: compute the semi-perimeter s = (a + b + c) / 2, then Area = √[s(s − a)(s − b)(s − c)]. This is enormously useful for irregular lots, where you can measure the boundary distances but cannot easily find a perpendicular height.
When you do know a base and its perpendicular height, the simpler formula applies: Area = ½ × base × height. Remember the height must be measured at a right angle to the base, not along a slanted edge.
A trapezoid has one pair of parallel sides. Area = (b1 + b2) / 2 × height — the average of the two bases times the perpendicular distance between them. Many land parcels and roof sections are trapezoids.
A sector is a pie slice of a circle. With the angle in degrees, Area = A / 360 × π × r²; with the angle in radians, Area = ½ × r² × A. Note this calculator asks for the radius here, not the diameter. Curved driveway sections and rounded corners are often sectors.
Area = base × height, using the perpendicular height rather than the slanted side. A rectangle is a parallelogram with right angles.
For a simple rectangular room, measure the length and the width at floor level and multiply. Measure to the inside face of the walls, and take each dimension in two places — rooms are rarely perfectly square, and an inch of difference over 20 feet matters.
For an irregular space, the reliable method is to divide and conquer: sketch the space, break it into rectangles, triangles, and trapezoids, calculate each piece separately, and add the results. Subtract areas you do not need to cover — a kitchen island, a fireplace hearth, a stairwell opening. For an L-shaped room, two rectangles are usually all you need. For a whole house, measure each room individually and total them; this is also how appraisers work, though they follow specific standards about what counts.
When square footage is quoted for real estate, it usually means gross living area — finished, heated space that is above grade. That distinction matters a great deal. A finished basement is typically not included in the headline square footage even though it is usable space, because it is below grade; it is listed separately. Garages, unheated porches, attics without finished access, and detached structures are also normally excluded. Stairs generally count on each floor they serve. Because the rules vary by market and appraiser, and because listings sometimes measure from exterior walls while a tape measure inside gives you interior dimensions, a home's advertised square footage and your own measurement can legitimately differ by several percent.
Once you know the area, ordering materials is straightforward — with one important caveat. Always add a waste allowance:
Use the price field to convert your area straight into a budget. Enter the price per square foot your supplier quotes, and the calculator does the multiplication for the full quantity you entered.
Few numbers carry as much weight in a property transaction as square footage. It is the basis for price per square foot, the metric buyers, sellers, and appraisers use to compare homes across a neighborhood, and it directly drives the valuation of both residential and commercial property. Commercial leases are almost always quoted per square foot per year, so an error of a few percent compounds into thousands of dollars over a lease term. Property taxes, insurance replacement costs, and even HVAC sizing all trace back to the same figure.
It matters just as much for anyone doing work on a home. Contractors bid by the square foot for flooring, tiling, painting, roofing, drywall, and landscaping, so knowing the area before you request quotes tells you immediately whether a bid is reasonable. It also lets you compare two proposals that are structured differently. And when you are buying materials yourself, the difference between measuring carefully and estimating by eye is usually the difference between one trip to the store and three.
For a rectangle, multiply length by width with both measured in feet. For other shapes, use the matching calculator above. If your measurements are in inches, meters, or another unit, just select that unit — the calculator converts and reports the result in square feet.
One acre equals 43,560 square feet, or about 4,046.86 square meters. A square mile contains 640 acres. Every result includes an acre conversion in the "Show result in other units" panel.
For the Circle and Ring calculators, enter the diameter — the full distance across. For the Sector calculator, enter the radius — the distance from the center to the edge. The labels on each field tell you which is expected.
It multiplies the area by however many identical surfaces you have. Enter 4 for four identical walls or windows and the calculator returns the total area, and the price estimate covers all of them.
Break it into simple shapes — rectangles, triangles, trapezoids — calculate each one separately, and add the results together. Subtract any areas you do not need to cover. This method handles almost any real-world floor plan.
Usually not in the headline figure. Real estate square footage normally means finished, heated space above grade, so below-grade basements are listed separately even when finished. Garages and unheated porches are typically excluded too, though conventions vary by market.
This Square Footage Calculator is provided for educational and general informational purposes. Results are computed with standard geometric formulas and displayed to high precision; round them as appropriate and add a waste allowance before ordering materials. Real estate square footage conventions vary by market and appraiser. For construction, land surveying, appraisal, or other critical work, always verify measurements independently.