Area Calculator

Most area calculators do one job and stop. You measure a room in feet, type it in, and get square feet back. That works right up until the flooring you want is priced per square meter, or the lot you are sizing needs to be in acres, and suddenly you are hunting for a second converter and second-guessing the math. So this calculator shows every unit at once. Every time it works out an area, it also gives you that same area in square inches, square feet, square yards, acres, and square miles, plus the metric side down to square millimeters and up to hectares and square kilometers. Each row has its own copy button.

Pick a shape, type the measurements, read the answer. Rectangle, square, circle, triangle (two ways), trapezoid, parallelogram, or an ellipse. It shows the exact formula it used, so the number isn't a black box and you can check it by hand. And it defaults to feet, because most people reaching for this are measuring a room, a wall, or a yard in feet.

1. Pick your shape from the dropdown. The input boxes change to match. A circle asks for a radius, a trapezoid asks for two bases and a height.
2. Set your unit. Feet is the default. Inches, yards, miles, meters, centimeters, millimeters, and kilometers are all in the list. This is the unit you measured in, and the tool treats every box as that same unit.
3. Enter the measurements. The area appears instantly below in your chosen unit squared, with the formula underneath.
4. Read it in every other unit. Under the main result sits the full conversion panel. Need square meters for a supplier or acres for a plot? It's already there. Hit Copy on any row, or Copy all to grab the whole set as a tidy list.
5. Share or bookmark it. The Share button copies a link that reopens this exact calculation, same shape, same unit, same numbers. Good for sending a measurement to someone, or saving a job you'll come back to.

Decimals are fine, type 2.5 for two and a half feet. Enter a negative and you get a friendly nudge, because a wall can't be minus three feet long.

This is the part I care most about, because it's where cheap calculators quietly let people down. Converting an area between units is not the same as converting a length, and the difference matters more than people expect.

The mistake comes from the units themselves. One foot is 0.3048 meters, so plenty of people assume one square foot is 0.3048 square meters, but it is actually 0.0929. You have to square the conversion factor too, because you're converting a two-dimensional thing rather than a line. Miss that and your answer is off by a factor of three, which is exactly how someone ends up ordering a third of the tile they needed. The all-units panel does the squaring correctly on every row, so you never touch that math yourself.

It's also why the answer always comes out squared. Multiply two lengths and the units multiply along with them. Feet times feet is square feet, written ft². A 3-foot by 4-foot patch is 12 square feet, not 12 feet. That little exponent is what makes the number an area instead of a length.

And square units grow faster than people expect. Double a room's dimensions and the floor area goes up four times over, not two. A 10 by 10 room is 100 square feet. A 20 by 20 room is 400, so four times the flooring and four times the paint. That's why a project's material cost balloons when you scale it up, and why getting the area right in the first place matters.

The panel also carries acres and hectares, which most basic tools leave out and which are the two things people measuring land actually want. A rectangular lot that comes to 87,120 square feet is 2 acres. You don't have to remember that an acre is 43,560 square feet, the row just reads 2.

You don't need these to use the tool, but knowing why each one works helps you catch a mis-measurement before it turns into a wrong order.

Rectangle. Length times width. Picture a grid of one-by-one squares laid over the shape. Five columns and four rows is twenty little squares, and that count is the area. A square is the same idea with equal sides, side times side.

Circle. π times the radius squared. The radius runs from the center to the edge, and the classic mistake is feeding it the diameter instead. If someone hands you the full width across, halve it first. A patio 10 feet across has a 5-foot radius, and an area of about 78.5 square feet.

Triangle. Half of base times height. Copy any triangle, flip the copy, and the two slot together into a rectangle, so a triangle is exactly half of one. The catch is that height means the perpendicular height, a straight line up from the base at a right angle, not the slanted edge. On a leaning triangle those are very different numbers.

Triangle from three sides. Sometimes you can't get a clean height, you're standing in a field with three stakes and a tape measure. Feed it the three side lengths and Heron's formula still finds the area. One rule the sides have to obey, any two of them added together must beat the third, or they can't close into a triangle and the tool tells you so.

Trapezoid. Average the two parallel sides, then multiply by the height. A trapezoid is basically a rectangle whose width is the average of its two ends.

Parallelogram. Base times height, a slanted rectangle. Shear it back upright and the area doesn't change, as long as the height is the perpendicular gap between the base lines and not the sloped side.

Ellipse. π times the two semi-axes, the long radius and the short one multiplied together with π. When the two match, you're back to a plain circle.

Real rooms and plots are rarely one clean shape. The move is always the same, chop the thing into pieces the tool already knows, work out each one, and add them up. An L-shaped room comes apart into two rectangles. A room with a rounded bay is a rectangle plus a half circle. A plot with an angled corner is a rectangle plus a triangle.

Cutting a hole out works in reverse. For a wall with a window, find the whole wall's area, find the window's area, and subtract. That's your paintable surface. Once every real shape reads as a sum or difference of rectangles, triangles, and circles, none of them are intimidating.

The one case this can't clean up is a genuinely irregular blob, a freeform pond, a wandering property line with no straight edges at all, and geometry has no formula waiting for that. Overlay a grid and count squares, or trace it in a mapping tool. This calculator handles the shapes geometry has names for, which is almost everything you'll actually measure.