Square Footage Calculator

What this square footage calculator does

This calculator works out the area of a space in square feet, square metres, and square yards. It supports five shapes — rectangle, circle, triangle, trapezoid, and an L- shape (two rectangles added together) — which between them cover almost every room, lot, patio, and garden bed you’ll need to measure. There’s no waste factor because pure geometry doesn’t need one; material-specific waste belongs on the calculator for the specific material (paint, flooring, sod, mulch).

How to use the square footage calculator

1. Pick the shape that best matches what you’re measuring. For a typical rectangular room, choose Rectangle. For a round patio or pool surround, Circle. For a triangular corner garden, Triangle. For a wedge-shaped lot or a beveled deck end, Trapezoid. For an L-shaped open-plan living area or any space that’s two rectangles joined at a corner, L-shape.
2. Enter the measurements in feet. The calculator accepts decimals (12.5 ft is fine), so converting a half-inch tape reading to feet is the only manual step.
3. Read the three results — square feet for US ordering, square metres for international ordering, and square yards for carpet and sod.
4. Tap Copy summary to put the result on your clipboard for a shopping list or supplier quote.

How to measure each shape correctly

Rectangles are the easiest: measure the length, measure the width, multiply. Measure to the inside face of the wall, not to the trim or baseboard. If a room is slightly out of square (older houses often are), measure the length and width at three points each — both ends and the middle — and average them.

Circles use diameter, not radius. Stretch the tape across the widest part of the circle, perpendicular to a wall or edge if there is one. For a perfectly round room, two measurements 90° apart should agree to within an inch; if they don’t, the room is closer to an oval and you should measure both axes and use the average.

Triangles need a base (any one side) and a perpendicular height (the distance from the base to the opposite vertex, measured at 90° to the base). Do NOT use the slanted side as the height — that’s a common mistake. If you’re measuring an outdoor triangular patch, drive a stake at the apex and use a string-line plus a carpenter’s square to get the perpendicular distance.

Trapezoids are the right choice for any four-sided shape with one pair of parallel sides. Wedge-shaped property lots, beveled deck corners, and curved-edge driveways all fit this pattern. Measure both parallel sides (base 1 and base 2) and the perpendicular distance between them (height).

L-shapes are two rectangles. Decide where you’ll split the L, measure each rectangle, and let the calculator add them. Take care not to double-count the shared edge — the rectangles share a corner, not an overlapping area.

Square feet vs square metres vs square yards

Most US flooring shops list both square feet and square yards on the product page so you can buy by whichever unit the manufacturer prefers. For paint, drywall, and most other construction materials, square feet is the universal unit.

Why measure twice

The single biggest source of error in DIY area calculations isn’t the arithmetic — it’s the measurement. A few habits prevent costly mistakes:

• Use a 25-foot tape, not a yardstick. Repeated short measurements accumulate error fast. A continuous pull is more accurate.
• Measure to the wall, not the baseboard. Baseboards add about half an inch on each side; over a long room, that’s a measurable amount.
• Sketch the room and write each dimension on the sketch. Doing the math from a half-remembered set of numbers in your head is how rooms end up an extra 5 sqft short.
• For carpet and tile, always order more than the calculator says. Patterns need to match, off-cuts go to waste, and a single bad plank or tile means another box. 10 % extra is the floor-covering industry’s standard add-on.

When to combine shapes

Real rooms and lots are rarely a single primitive. A typical use case: measuring the floor area of a kitchen with a peninsula. Treat the open kitchen as a rectangle, add the peninsula as a second rectangle, but subtract any closet or pantry footprint that doesn’t get the same flooring. The calculator’s L-shape option covers the most common add-rectangle case; for subtractions, run the calculator twice and subtract the smaller area from the larger one by hand.

Privacy

This calculator does its arithmetic in JavaScript on your device. There is no fetch call, no analytics on the values you enter, no server-side logging. The page works the same way offline once loaded.