Square Footage Calculator

What the square footage calculator does

Square footage is the number behind nearly every material order, from flooring to paint to turf, so getting it right is where most projects start. This works it out. You pick a shape, enter its size, and it returns the area in square feet, with options for a border, a quantity, and a price.

It handles four shapes and a couple of extras that save you a second calculation. Below is how it works.

How to use it

1. Pick the shape: rectangle, square, circle, or triangle.
2. Enter its size for that shape, each measurement with its unit.
3. Tick a border, set a quantity, or add a price if you need them, then press Calculate, or Reset to clear it.

How the area is worked out

Each shape has its own area formula, and the calculator converts your measurements to feet first, so the answer always lands in square feet whatever unit you enter. For the simplest case, a rectangle:

Square feet = length × width

For a room or plot that is not a single shape, work out each part separately and add them together. The other shapes follow their own formulas, which the next section covers.

The four shapes

The shapes cover the outlines most jobs come in. A rectangle is length times width, and a square is just a side times itself. A circle uses pi times the radius squared, worked from the diameter you enter, for round patios and beds.

A triangle is the clever one: rather than asking for a base and a height, which are awkward to measure on the ground, it takes the three side lengths and finds the area from them using a classic formula. That suits a real plot, where measuring the three sides is far easier than finding the perpendicular height. Pick the shape that matches and the right formula is used.

The border and quantity options

The border option is for when you want the area of a frame rather than a whole shape, a path around a patio, or a margin around a bed. It works out the area as the outer shape minus the inner space the border surrounds, leaving just the band itself, which is exactly what you need to order edging or a walkway.

The quantity option multiplies the area by however many identical shapes you have, so several rooms of the same size, or a run of matching beds, come out in one go. Add a price as well and it totals the cost. Together they turn a single area into a full order without reaching for a separate sum.

A worked example: a 12 by 15 room

Say the room is a rectangle 12 feet by 15 feet.

The area is 12 × 15 = 180 square feet. If you had four identical rooms, the quantity option would give 4 × 180 = 720 square feet, and a price per square foot would total the lot.

Or for a 2 foot path around a 20 by 20 patio, the border option gives the outer 400 square feet minus the inner 256, leaving 144 square feet of path.

Questions people ask

How do I calculate square footage?

For a rectangle, multiply length by width in feet. A 12 by 15 foot room is 180 square feet. Other shapes use their own area formulas, which the calculator applies.

Can it handle circles and triangles?

Yes. A circle uses pi times the radius squared, and a triangle is worked out from its three side lengths, which are easier to measure than a height.

What is the border option for?

It finds the area of a frame or path, the outer shape minus the inner space it surrounds, so you can order edging or a walkway.

How do I measure an irregular room?

Split it into rectangles, squares, and triangles, work out each one, and add the areas together.

References

A quick note on the numbers. The areas are plain geometry: length times width for rectangles, pi times the radius squared for circles, and the three-side formula for triangles. The unit conversions used to bring every measurement to feet follow the US National Institute of Standards and Technology guide.

1. National Institute of Standards and Technology (NIST), Special Publication 811, Guide for the Use of the International System of Units (SI). https://www.nist.gov/pml/special-publication-811