Enter the dimensions of a rectangle, circle, triangle or trapezoid in feet, inches, yards or meters to get the area in every common unit. Add a quantity for identical rooms or tiles, and an optional cost per square foot to see a total price.
Updated September 2026 · Formulas and unit factors are shown on the page.
Identical rooms, tiles or panels
| Unit | Area |
|---|
Every shape reduces to one formula. A rectangle or square is length × width: a 12 ft by 10 ft room is 120 sq ft. A circle is π × (diameter ÷ 2)²: a 10 ft diameter circle is 78.54 sq ft. A triangle is ½ × base × height: a 10 ft base with an 8 ft height is 40 sq ft. A trapezoid is ½ × (top + bottom) × height: parallel sides of 8 ft and 12 ft with a 6 ft height in between comes to 60 sq ft. The calculator above runs these same formulas — pick a shape, enter the dimensions, and the area, conversions and (if you enter a price) the cost update together.
Tape measures read in feet and inches, not decimal feet, so the calculator has a "Feet + inches" unit with a companion inches box next to each dimension. Twelve feet six inches is 12.5 ft, because 6 in ÷ 12 = 0.5 ft. If you only have a measurement in inches, divide the area in square inches by 144 (12 × 12) to get square feet: a 150 in by 120 in space is 18,000 sq in, and 18,000 ÷ 144 = 125 sq ft.
A rectangular room is a single calculation, but an L-shaped room is not. Split it into two or more rectangles, work out each one with the formula above, and add the results — the calculator's quantity field does the same thing when several rooms, tiles or panels share the same dimensions, multiplying one shape's area by however many identical pieces you have.
A house's listed square footage is the sum of its finished rooms, not the size of the lot or the footprint of the building. The standard most US listings follow measures finished, above-grade living space from the exterior walls, and leaves out garages, unfinished basements and unfinished attics — so two houses with the same footprint can have very different listed square footage depending on what is finished. To total several rooms with different dimensions in one go, the room square footage calculator adds up to six rooms at once.
Once you have the area, a total cost is just area × price per square foot. On the default 12 ft by 10 ft room (120 sq ft) at $3.50 per square foot — an illustrative figure, not a market price — the total is 120 sq ft × $3.50 = $420.00. Enter your own quote in the cost field to see your own total; the calculator does not supply or suggest a price. To go the other way — a total price divided by an area, or two properties compared per square foot — use the price per square foot calculator .
A quick reference for typical rectangular room dimensions, computed the same way as the calculator above.
| Room size | Sq ft | Sq yd | m² |
|---|---|---|---|
| 10 × 10 ft | 100 | 11.11 | 9.29 |
| 10 × 12 ft | 120 | 13.33 | 11.15 |
| 12 × 12 ft | 144 | 16 | 13.38 |
| 12 × 14 ft | 168 | 18.67 | 15.61 |
| 12 × 15 ft | 180 | 20 | 16.72 |
| 14 × 16 ft | 224 | 24.89 | 20.81 |
| 15 × 20 ft | 300 | 33.33 | 27.87 |
| 20 × 20 ft | 400 | 44.44 | 37.16 |
For land instead of a room, the square feet to acres calculator converts a lot's square footage to acres and back, and the roof square footage calculator turns a house footprint and roof pitch into roofing squares and shingle bundles.
Measure the length and width in feet and multiply them: length × width. A 12 ft by 10 ft room is 120 sq ft. If a wall is not straight, split the room into rectangles, work out each one, and add the results together.
A 12 ft by 12 ft room is 144 sq ft — 12 × 12. That is also 16 sq yd and 13.38 m².
Convert each dimension to feet by dividing by 12, then multiply, or work in inches and divide the result by 144 (12 × 12). A 150 in by 120 in space is 125 sq ft: 150 × 120 = 18,000 sq in, and 18,000 ÷ 144 = 125.
An acre is 43,560 square feet. Use the square feet to acres calculator to convert a lot size or a specific square-footage figure both ways.
Area = π × (diameter ÷ 2)². A circle with a 10 ft diameter has a 5 ft radius, so the area is π × 5² = 78.54 sq ft.
Most US listings follow the standard of measuring finished, above-grade living space from the exterior walls — garages, unfinished basements and unfinished attics are left out. Add up each finished room (use the quantity field here for identical rooms) to get the total.
Add up to six rooms into one total, in feet, feet + inches or meters.
Divide a price by square footage, or compare two properties per square foot.
Estimate roof area from the house footprint and pitch, plus roofing squares and shingle bundles.
Convert square feet to acres and back, or enter a lot’s length and width.