Square Footage Calculator

How to use these calculators

Each shape above is its own calculator, so an answer stays on screen while you work out the next one — useful when a job is a patio plus the path around it, or a floor plus a bay window.

1. Pick the shape that matches the area you are measuring.
2. Enter each measurement and choose the unit beside it. Every measurement has its own unit, so a length in feet and a width in inches are fine together.
3. Set the quantity if you have several identical areas, and optionally a price per square foot, square yard, square metre or acre.
4. Press that shape's Calculate button. The result is in square feet, with the same area in square inches, square yards, square metres and acres beneath it.

The nine formulas

Every measurement is converted to feet first, then the shape's formula applies:

• Rectangle — length × width.
• Rectangle Border — the outer rectangle less the rectangle left inside the border, which sits inside the dimensions you enter: (l × w) − (l − 2b) × (w − 2b).
• Circle — π × (diameter ÷ 2)².
• Ring — the outer disc less the disc inside the border: π × (r² − (r − b)²).
• Triangle with Edge Lengths — Heron's formula from the three sides, with s = (a + b + c) ÷ 2: √(s(s − a)(s − b)(s − c)).
• Triangle with Base & Height — (base × height) ÷ 2.
• Trapezoid — ((base 1 + base 2) ÷ 2) × height.
• Sector — (angle in radians ÷ 2) × radius², so a 90° wedge is a quarter of the circle.
• Parallelogram — base × perpendicular height, not the slanted side.

A worked example

A bedroom 12 ft long and 15 ft wide is 12 × 15 = 180 square feet, which is about 16.7225 square metres or exactly 20 square yards. Set the quantity to 2 for a pair of identical rooms and the total becomes 360 square feet; enter a flooring price of $3.50 per square foot and the estimate is 360 × 3.50 = $1,260 before any waste allowance.

Square footage conversions

Different materials are sold in different units, so it helps to know the equivalents:

Unit	In square feet
1 square inch	0.00694 sq ft
1 square foot	1 sq ft
1 square yard	9 sq ft
1 square metre	10.7639 sq ft
1 acre	43,560 sq ft

These follow from one definition: a foot is exactly 0.3048 metres. That is where 10.7639 comes from, and why the figures above are computed from it rather than from a rounded factor.

Measuring a room accurately

Run a tape measure or laser measure along the longest wall for the length and the widest wall for the width, at floor level. Round to the nearest few inches — flooring and paint are estimates, not engineering. Measure into doorways and closets only if you intend to floor them. A quick sketch with each wall's length noted saves re-measuring later.

L-shaped and irregular rooms

Any awkward shape becomes easy once you break it into pieces:

• Divide the floor plan into rectangles, triangles and circles.
• Calculate each piece with the matching calculator above.
• Add the totals together.

An L-shaped living room is just two rectangles — say a 12 × 15 main area (180 sq ft) plus a 6 × 8 alcove (48 sq ft) for 228 sq ft in total. A room with a rounded bay is a rectangle plus a sector.

Estimating materials and cost

For flooring, tile or paint, take your total square footage and add about 5–10% for waste, offcuts and mistakes, then enter a price for a cost estimate. Price in whatever unit your supplier quotes — carpet by the square yard, tile by the square metre, land by the acre — and the conversion is handled for you. For a slab you're pouring rather than a floor you're covering, the concrete calculator works in cubic yards and bags.