Square Foot Calculator: Feet to Sq Ft
- Length
- 12 ft
- You entered
- Width
- 10 ft
- You entered
This calculator works out the area of a rectangular space in square feet when you enter its length and width in feet. Type in the two dimensions and it returns the total square footage, which is the number you need for flooring, tiling, painting, or estimating room size. The result is given in square feet (ft²), and the same formula applies whether you measure in feet or convert from inches or yards first.
Formula
The area of a rectangle is length times width:
Area (ft²) = Length (ft) × Width (ft)
Where:
- Length is the longer side of the rectangle, measured in feet.
- Width is the shorter side, also in feet.
- Area is the result in square feet (ft²).
If your measurements are in inches, divide each by 12 to get feet first. If they are in yards, multiply each by 3 to get feet.
Worked Example
Using the default values from the calculator: length = 12 ft, width = 10 ft.
- Write the formula: Area = Length × Width
- Substitute the numbers: Area = 12 ft × 10 ft
- Multiply: Area = 120 ft²
The calculator shows 120.00 sq ft, matching the manual result.
How to Use the Square Foot Calculator
Enter the length and width of your space in feet into the two input boxes, then read the area. The calculator assumes a perfect rectangle, which covers most rooms, floors, walls, and yards. For an L-shaped room, split it into two rectangles, calculate each area, and add them together. For a circular area, use a different formula (π × radius²) with the radius in feet.
Common uses include:
- Buying flooring or carpet – you need the floor area in square feet.
- Painting walls – measure each wall’s length and height, then sum the areas.
- Lawn or garden treatments – calculate the area to know how much product to buy.
- Real estate listings – rooms are often advertised in square feet.
Common Mistakes and How to Avoid Them
The most frequent error is mixing units. If you measure one side in feet and the other in inches, the result will be wrong. Always convert to the same unit before multiplying. For example, a 10 ft by 6 ft room is 60 ft², but if you mistakenly use 10 ft × 6 in (0.5 ft), you get 5 ft² – a huge difference.
Another mistake is forgetting to account for waste when buying materials. For flooring or tile, add 10% extra to cover cuts and mistakes. For paint, check the coverage per gallon on the label – typically 350–400 ft² per gallon for one coat.
Rounding: if your measurements are not whole numbers, keep the decimals until the final answer. Rounding early can cause noticeable errors in large areas.
When to Use Square Feet vs. Other Units
Square feet is the standard unit for real estate and construction in the United States and Canada. In most other countries, square meters are used. To convert square feet to square meters, multiply by 0.092903. To convert square meters to square feet, multiply by 10.7639. For very large areas (acres), remember 1 acre = 43,560 ft².
If you are working with a blueprint that lists dimensions in feet and inches, convert the inches to a decimal foot (e.g., 6 inches = 0.5 ft) before multiplying.
Limitations of the Formula
The length × width formula only works for rectangles. For triangles, use (base × height) / 2. For circles, use π × radius². For irregular shapes, break them into rectangles and triangles, calculate each, and sum. The calculator also assumes a flat, two-dimensional area – it does not account for sloped ceilings, curved walls, or three-dimensional features.
For a room with a bay window or alcove, measure the main rectangle separately and add the alcove’s area. Always measure from wall to wall, not from baseboard to baseboard, because baseboards add a few inches that can change the total.
Frequently Asked Questions
How do I calculate square footage from inches?
First convert each measurement from inches to feet by dividing by 12. For example, a 24-inch by 36-inch area becomes 2 ft by 3 ft, giving 6 ft². Alternatively, multiply the inches together and divide by 144 (since 1 ft² = 144 in²).
What is the difference between square feet and feet?
Feet measure length – a single dimension. Square feet measure area – a two-dimensional space. A room that is 10 feet long and 12 feet wide has a perimeter of 44 feet but an area of 120 square feet. You cannot convert directly between them without knowing the other dimension.
How many square feet is a 10×10 room?
A 10×10 room means 10 feet by 10 feet, so the area is 100 square feet. This is a common size for a small bedroom or home office.
Do I need to include closets in square footage?
For real estate listings, closets are usually included in the total square footage of a home. For buying flooring or paint, you should measure the closet separately if you plan to cover it, or exclude it if you don’t. Always clarify with your agent or contractor.
How do I measure a room with slanted walls?
For a room with a slanted ceiling (like an attic), measure the floor area normally. For walls, measure the height at the tallest point and the width, then calculate the area as a rectangle – this gives a slight overestimate, which is fine for paint estimates. For exact material, measure the actual wall shape.