Square Foot Calculator
Find the area or missing side of a rectangular floor or wall, then estimate cost at your price.
Area, Missing Side & Cost
Use feet, or feet and inches such as 12'6".
Enter area in sq ft; known length accepts feet and inches.
Your Result
Missing side: ft (width)
Square feet (sq ft)
- Square yards (sq yd)
- Square meters (m²)
Results are rounded to 2 decimal places.
Estimated cost
Illustrative estimate only — not a quote.
Find a Missing Side from Square Feet
If you know the area of a rectangular room and one side, you can find the other side by dividing the area by the known measurement. Choose Find missing side, enter the area in square feet, and enter the known length in feet. The result gives the remaining dimension, which is the width for a floor or the height for a wall.
For example, a rectangular room covering 144 square feet with a known length of 12 feet has a width of 12 feet: 144 ÷ 12 = 12. A 300 square foot rectangle with a length of 15 feet has a width of 20 feet: 300 ÷ 15 = 20. Both examples use the entire area of a single rectangle.
This reverse calculation works only for rectangles. An irregular outline, a missing corner, or an area that includes several spaces cannot reliably provide one unknown side. Check that the known measurement belongs to the same surface as the area. Area alone is insufficient: without a known side, many different length and width combinations can fit the same total.
Floor vs Wall Area: Which Dimensions to Measure
Select Floor when measuring the horizontal surface beneath your feet. Measure its length and width between the boundaries of the rectangular section you intend to cover. Furniture does not change the floor's dimensions, but a built-in feature may affect the surface included in your project. Decide those boundaries before recording measurements.
Select Wall when measuring a vertical surface. Measure horizontally along the wall for length, then vertically from the bottom to the top for height. The calculator changes its second field to Height to match that measurement. In missing-side mode, a wall's known length and area determine its height.
A wall result represents the full rectangle. Doors, windows, sloping ceilings, and other openings require separate adjustments to the measured surface. Floor area cannot stand in for wall area: even rooms with identical floors can have different wall heights.
| Surface | Dimensions to measure | Used for |
|---|---|---|
| Floor | Length × width | Flooring, carpet, and floor tile |
| Wall | Length × height | Paint, wallpaper, and wall tile |
Cost per Square Foot: Quick Reference
Use this reference to compare a few hypothetical prices against common project sizes. Find your area across the top and a sample unit price down the left. Each intersection shows an illustrative total in dollars. For your own figures, enter a price in the calculator. These examples do not establish market rates or include unlisted project charges, taxes, or extras.
Example unit prices only — not quotes.
| Price per sq ft | 100 sq ft | 200 sq ft | 500 sq ft | 1,000 sq ft |
|---|---|---|---|---|
| $1 | $100 | $200 | $500 | $1,000 |
| $2 | $200 | $400 | $1,000 | $2,000 |
| $3 | $300 | $600 | $1,500 | $3,000 |
| $5 | $500 | $1,000 | $2,500 | $5,000 |
| $8 | $800 | $1,600 | $4,000 | $8,000 |
Square Foot Calculator FAQ
How do I calculate square footage of a room?
For a rectangular room, choose Find area and Floor, then enter its length and width in feet. The calculator displays the floor area immediately. Measure only the rectangle you want to include; this page calculates one room or surface at a time.
How many square feet is a 12x12 room?
A rectangular room measuring 12 feet by 12 feet covers 144 square feet. That total describes its floor, not its walls. To measure a wall in the same room, select Wall and use the wall's length and height.
How do I convert square feet to square yards?
Divide square feet by 9 to get square yards. For example, 144 square feet equals 16 square yards. This calculator displays both units together, so you can read the converted area directly after entering dimensions or a known area.
How do I find the missing side of a room if I know the square footage?
Select Find missing side and enter the rectangular room's area and known length. The missing width is the area divided by that length. For example, 300 square feet divided by 15 feet gives a width of 20 feet.
What is the difference between floor area and wall area?
Floor area measures a horizontal surface using length and width. Wall area measures a vertical surface using length and height. Selecting Wall changes the dimension label accordingly. A room's floor area does not tell you the combined area of its walls.
How do I calculate square feet for painting a wall?
Select Find area and Wall, then enter the wall's horizontal length and vertical height. The result is the full rectangular wall area. If your project excludes doors or windows, subtract those opening areas separately before estimating the surface to paint.
How much does 1,000 square feet cost at $3 per square foot?
At an entered price of $3 per square foot, 1,000 square feet gives an illustrative total of $3,000. This assumes the price applies to the entire measured area. It is not a quote and excludes any charges absent from your unit price.
Can I use square feet to work out both length and width?
No. Area alone does not determine both dimensions of a rectangle. For example, 144 square feet could measure 12 by 12 feet or 9 by 16 feet. You need a known side or another constraint to identify a specific pair.