📚 What's in This Guide
This square footage calculator finds the area of a room, wall, lot, or any mix of shapes in square feet. Enter lengths in feet and inches, or in meters and centimeters, add as many areas as you need, and set any area to Subtracted to take out a closet, a cutout, or a window. The total appears in square feet, square inches, square yards, square meters, and acres, with optional waste, boxes, and cost. If you searched for a square foot calculator, a sq ft calculator, a sqft calculator, or a square feet calculator, this is the same tool.
Below you will find the formulas, measuring steps, worked examples, and a plain explanation of how the official square footage of a home is measured, which is not always the same as adding up room sizes.
Square footage = length × width, with both in feet. A room 12 ft by 10 ft is 120 sq ft. For an irregular shape, split it into rectangles and add them, or subtract the missing part from a larger rectangle.
1. How the Square Footage Calculator Works
The calculator is built around a list of areas. Each area has an optional name, a shape, a quantity, and the measurements for that shape. You choose whether the area is Added or Subtracted. The calculator works out the area of each shape from its standard formula, multiplies by the quantity, adds the added areas, and takes away the subtracted ones.
There are five shapes: rectangle or square, triangle from a base and height, triangle from three sides, circle, and trapezoid. Other shapes are built from these. A ring or a border is a big shape with a smaller one subtracted. An L-shape is two rectangles, or one rectangle with a corner subtracted.
Each measurement has two boxes, feet and inches, or meters and centimeters, so you can type 14 ft 6 in exactly as you read it from the tape. The results show the total in your chosen system first, then the same area in the other units. If you fill in the optional fields, you also get the area to order with waste, the number of boxes, and an estimated cost.
The calculator measures flat, two-dimensional area. It does not measure walls that slope, curved edges that are not circles, or volume. For rounded or free-form shapes, approximate with several simple shapes. The result is a planning estimate. For a legal or appraisal square footage, a professional measurement governs.
2. How to Use the Square Footage Calculator
- Choose feet and inches, or meters and centimeters.
- Pick the shape of your first area. For a normal room, leave it on Rectangle.
- Type the measurements. Leave the inches or centimeters box empty if it is zero.
- Give the area a name if you like, such as Living room, and set a quantity if you have several identical areas.
- Use Add Another Area for each extra room or section, up to 12.
- Set an area to Subtracted if it should be taken out, such as a closet, a stair opening, or a cutout.
- Optionally add a waste percentage, the coverage of one box, and a price per unit of area.
- Read the total, the unit cards, the breakdown table, and the step-by-step math. Use the Convert Area tab to change any known area between units.
- Use Copy Result, Share Result, or Download PDF to keep the numbers, and Reset All to start again.
If a required field is blank, an area is incomplete, or a quantity is not a whole number, the calculator tells you which area needs attention and leaves it out until you fix it. If the three sides of a triangle cannot form a triangle, it says so instead of showing a number.
3. Square Footage Formulas
All formulas below use feet, so the answer comes out in square feet. Convert every measurement to feet before you multiply.
| Shape | Formula | What you measure |
|---|---|---|
| Rectangle or square | length × width | Two adjacent sides |
| Triangle (base and height) | ½ × base × height | One side and the straight-line height to it |
| Triangle (three sides) | √[s(s − a)(s − b)(s − c)], where s = (a + b + c) / 2 | All three sides |
| Circle | π × (diameter / 2)² | Diameter across the middle |
| Trapezoid | ½ × (base 1 + base 2) × height | The two parallel sides and the height between them |
| Ring or border | outer area − inner area | Add the outer shape, subtract the inner one |
The three-side triangle formula is known as Heron's formula. A triangle with sides 13, 14, and 15 ft has s = 21, so the area is √(21 × 8 × 7 × 6) = √7,056 = 84 sq ft. If the two shorter sides do not add up to more than the longest side, no triangle exists.
4. How to Measure the Square Footage of a Room
- Clear the edges. Move furniture away from the walls so the tape can reach the wall surface.
- Measure wall to wall. Measure the length and the width across the floor from one wall surface to the opposite one.
- Measure at more than one point. Older rooms are rarely perfectly square. If two measurements of the same wall differ, use the larger value for ordering material and the average for a size estimate.
- Write down feet and inches exactly. A reading of 14 ft 6 in goes in as 14 and 6, not 14.6.
- Note every jog. Alcoves, bay windows, closets, and chimney breasts each become their own small area, added or subtracted.
For paint, drywall, or wallpaper, the surface you want is the wall, so measure its height from floor to ceiling and its length, then subtract openings. See the section on walls below.
5. Feet and Inches to Decimal Feet
This is where many hand calculations go wrong. An inch is one twelfth of a foot, so 6 inches is 0.5 ft, not 0.6 ft. To convert, divide the inches by 12 and add them to the feet. The calculator does this for you when you use the two boxes, but the table is handy for checking by hand.
| Inches | Decimal feet | Inches | Decimal feet |
|---|---|---|---|
| 1 in | 0.083 | 7 in | 0.583 |
| 2 in | 0.167 | 8 in | 0.667 |
| 3 in | 0.250 | 9 in | 0.750 |
| 4 in | 0.333 | 10 in | 0.833 |
| 5 in | 0.417 | 11 in | 0.917 |
| 6 in | 0.500 | 12 in | 1.000 |
For example, 14 ft 6 in is 14.5 ft and 11 ft 3 in is 11.25 ft. Treating 14 ft 6 in as 14.6 ft would overstate this room by about 1.1 square feet. Across a whole floor, mistakes like this add up.
6. L-Shaped and Irregular Rooms
Most rooms that are not rectangles can be handled with rectangles. There are two reliable ways, and they give the same answer.
Method 1: split and add. Draw a line that cuts the room into rectangles. Find each area and add them.
Method 2: enclose and subtract. Measure the smallest rectangle that would contain the whole room, then subtract the corner that is missing.
Take an L-shaped room that fits inside an 18 ft by 14 ft rectangle, with a 6 ft by 5 ft corner missing. Splitting it gives a bottom section of 18 × 9 = 162 sq ft and a top section of 12 × 5 = 60 sq ft, which adds up to 222 sq ft. Enclosing it gives 18 × 14 = 252 sq ft, minus 6 × 5 = 30 sq ft, which is also 222 sq ft. In the calculator, either enter two Added rectangles, or one Added rectangle and one Subtracted rectangle. Running both methods is a good check.
7. Walls, Doors, and Windows
To find the area of a wall, multiply its length by its height, then subtract each opening you will not cover. Take a wall 16 ft long and 8 ft high, with a door 3 ft by 7 ft and a window 4 ft by 3 ft. The wall is 16 × 8 = 128 sq ft. The door is 21 sq ft and the window is 12 sq ft, which is 33 sq ft in total. The area to paint is 128 − 33 = 95 sq ft.
In the calculator, add the wall as an Added rectangle, then add the door and the window as Subtracted rectangles. If a wall has four identical windows, add one window and set its quantity to 4. Whether to subtract small openings is a judgment call. If you want a little extra margin for trim and touch-ups, you can leave very small openings in and subtract only the large ones.
8. Worked Examples
A bedroom in feet and inches, with waste, boxes, and cost
A bedroom is 14 ft 6 in long and 11 ft 3 in wide. You will lay plank flooring that comes in boxes covering 20 sq ft each, costs $3.50 per square foot, and needs 10% waste.
| Step | Calculation | Result |
|---|---|---|
| Length in feet | 14 + 6/12 | 14.5 ft |
| Width in feet | 11 + 3/12 | 11.25 ft |
| Floor area | 14.5 × 11.25 | 163.13 sq ft |
| Area to order | 163.125 × 1.10 | 179.44 sq ft |
| Boxes | 179.44 / 20 = 8.97, rounded up | 9 boxes |
| Cost on the area to order | 179.44 × $3.50 | $628.03 |
Boxes are rounded up, but the cost uses the area to order, so buying 9 whole boxes may cost slightly more in practice, because you pay for full boxes.
A room in meters
A room is 4.2 m by 3.6 m. The area is 4.2 × 3.6 = 15.12 sq m. To get square feet, multiply by 10.7639, which gives about 162.75 sq ft. In the calculator, switch to Metric, type 4 m 20 cm and 3 m 60 cm, and the same total appears in both systems.
A circular patio
A round patio has a diameter of 10 ft. The radius is 5 ft, so the area is π × 5² = 78.54 sq ft. Choose Circle, type 10 ft in the Diameter box, and the calculator returns 78.54 sq ft.
9. Square Footage of a House
There are two different numbers people call a house's square footage, and they are not the same.
The sum of the rooms. For flooring, paint, or furniture planning, you add the interior floor area of each room. For a small single-floor home, that might look like this: living room 16 × 14 = 224 sq ft, kitchen 12 × 10 = 120, bedroom one 13 × 12 = 156, bedroom two 11 × 10 = 110, bathroom 8 × 6 = 48, and hallway 10 × 3.5 = 35. The total is 693 sq ft of room floor area. Add each room as its own named area to see the running total.
The official figure. For appraisals of single-family homes, the standard is ANSI Z765-2021, and Fannie Mae requires appraisers to follow it for most single-family appraisals. Its rules, as Fannie Mae's published guidance on the ANSI standard explains, include these points:
- Finished areas must have a ceiling height of at least 7 ft. In a room with a sloping ceiling, at least half of the finished area must be 7 ft or higher, and no part under 5 ft counts.
- Staircases are included in the floor from which they descend.
- Any space that is partly or fully below grade is reported as below-grade area, not above-grade living area.
- Openings to the floor below, such as a two-story foyer, are not included.
- The sketch uses exterior dimensions measured to the nearest tenth of a foot, and the final figure is reported to the nearest whole square foot.
Because the standard measures the outside of the house, the official number is usually larger than the sum of the rooms, which excludes wall thickness. Square footage from listings and tax records may have been measured in other ways, so numbers for the same house often disagree. The guidance applies to single-family homes, including townhouses. Apartments and condos in multifamily buildings are treated differently, with interior measurements. Local rules can vary.
To estimate the figure for your own house, enter the outside dimensions of each floor as areas and subtract anything that does not count, such as an unfinished section. This gives a planning number only. For a sale, an appraisal, or a legal document, use a professional measurement.
10. Waste, Boxes, and Cost
Area is exact, but material is not. Cuts, mistakes, and damaged pieces mean you need more than the floor area. The waste field adds a percentage to the net area and shows the result as the area to order. Leave it at 0 when you only want the size of the space.
| Situation | Typical planning waste |
|---|---|
| Simple rectangle, straight layout | 5 to 10% |
| Diagonal, tile, or rooms with many cuts and corners | 10 to 15% |
| Patterned or directional material that must line up | 15% or more |
These are planning figures, not rules. Always follow the product's instructions and your installer's advice. To get a box count, enter the coverage printed on one box. The calculator divides the area to order by that coverage and rounds up. Enter a price per square foot, or per square meter in metric mode, to see an estimated cost on the area to order.
11. Converting Area Units
The Convert Area tab changes an area between square inches, square centimeters, square feet, square yards, square meters, and acres. These are the factors it uses.
| Unit | Equals |
|---|---|
| 1 square foot | 144 square inches |
| 1 square yard | 9 square feet |
| 1 square meter | 10.7639 square feet |
| 1 square foot | 929.03 square centimeters |
| 1 acre | 43,560 square feet |
To change square inches to square feet, divide by 144. For example, 2,500 sq in is 2,500 / 144 = 17.36 sq ft. To change square meters to square feet, multiply by 10.7639, so 50 sq m is about 538.2 sq ft. To change acres to square feet, multiply by 43,560, so 2 acres is 87,120 sq ft. To go the other way from square feet to acres, divide by 43,560.
12. Common Mistakes
- Writing 14 ft 6 in as 14.6. Use 14.5, or use the two boxes in the calculator.
- Mixing units. Multiplying feet by inches gives a meaningless number. Convert first.
- Confusing square feet with feet or cubic feet. Square feet measure flat area. Feet measure length, and cubic feet measure volume.
- Forgetting to subtract openings when you are buying paint or wall material.
- Using the diameter as the radius in the circle formula.
- Treating the sum of the rooms as the official house size. The two figures are measured differently.
- Ordering the exact area. Add waste when you are buying material.
13. Related Calculations and Use Cases
Area is the starting point for most material estimates. Once you know the square footage, flooring, tile, and paint estimates are a matter of coverage and waste. For loose materials such as gravel, you multiply the area by a depth to get volume, which our Gravel Calculator does for you.
14. Frequently Asked Questions
Measure the length and width of the space in feet, then multiply them. A room 12 feet long and 14 feet wide is 12 x 14 = 168 square feet. If your measurements are in feet and inches, convert the inches to a decimal of a foot first (divide by 12). For triangles, circles, and irregular spaces, use the matching area formula, or split the space into simple shapes and add the areas.
A 12 ft by 14 ft room is 168 square feet. That is 12 x 14 = 168. In metric, 168 square feet is about 15.6 square meters.
Use one of two methods. Either split the room into rectangles, find each area, and add them, or measure the smallest rectangle that encloses the whole room and subtract the missing corner. Both give the same answer. In the calculator, add each rectangle as its own area, or add the big rectangle and set the missing corner to Subtracted.
Divide the number of square inches by 144, because one square foot is 12 inches by 12 inches, which is 144 square inches. For example, 2,500 square inches is 2,500 / 144 = 17.36 square feet. The Convert Area tab in the calculator does this for square inches, square centimeters, square yards, square meters, and acres.
One acre is 43,560 square feet. To convert square feet to acres, divide by 43,560. For example, a lot of 21,780 square feet is 0.5 acre, and 2 acres is 87,120 square feet.
For a home's official figure, a garage is not counted as living area, and closets, hallways, and stairs inside the finished living space are. Under the ANSI Z765-2021 method used by appraisers, only finished above-grade space with enough ceiling height counts, and finished below-grade space is reported separately. Listing and tax records may use different methods, so the numbers can differ.
Divide the inches by 12 and add the result to the feet. For example, 14 ft 6 in is 14 + 6/12 = 14.5 ft, and 11 ft 3 in is 11 + 3/12 = 11.25 ft. A common mistake is writing 14 ft 6 in as 14.6, which is wrong because an inch is one twelfth of a foot, not one tenth.
Conclusion
This square footage calculator turns a few measurements into a reliable area, whether you are sizing a single room, planning floor material, or adding up a whole floor plan. Enter feet and inches the way you read them from the tape, split irregular spaces into simple shapes, subtract what you will not cover, and add waste only when you buy material. Remember that a home's official square footage follows its own standard, so use the right number for the right purpose and confirm important measurements before you order or sign anything.
This calculator is for planning purposes only. Confirm measurements and material quantities before ordering. A professional measurement governs for appraisals, listings, and legal use.