How to use this calculator
- Choose your unit: feet, inches or meters.
- Choose how many areas you want to add up (1 to 4).
- For each area, pick a shape and enter its measurements:
- Rectangle: length and width.
- Circle: diameter, the distance straight across through the center.
- Triangle: base and height, measured at a right angle to the base.
- Trapezoid: the two parallel sides and the distance between them.
- Optionally enter a price per square foot and a waste allowance.
The result shows the total area in square feet, square meters and square yards, the amount to buy with waste, the estimated cost, and a table with each area.
Area formulas
Measurements in inches are converted by dividing square inches by 144. Measurements in meters are converted using 1 square foot = 0.09290304 square meters (exact, since 1 foot is defined as 0.3048 meters).
Worked example
Suppose you’re flooring a 15 × 12 foot living room, a round reading nook 8 feet across, and a bay window area shaped like a trapezoid, 6 feet wide at the wall, 10 feet at the room side and 4 feet deep. The flooring costs $3.50 per square foot.
- Living room: 15 × 12 = 180 sq ft.
- Nook: π × (8 ÷ 2)² = 50.27 sq ft.
- Bay: (6 + 10) ÷ 2 × 4 = 32 sq ft.
- Total: 180 + 50.27 + 32 = 262.27 sq ft, which is 24.37 m² or 29.14 square yards.
- With 10% waste: 262.27 × 1.1 = 288.49, so buy 289 sq ft.
- Cost: 288.49 × $3.50 ≈ $1,010.
If the shapes overlap in real life, measure them so they don’t, or you’ll count the same floor twice. The table under the result lists each area separately, so you can check every piece against your sketch.
Common room sizes
| Room size | Square feet | Square meters | Square yards | With 10% waste |
|---|---|---|---|---|
| 10 × 10 ft | 100 | 9.29 | 11.11 | 110 |
| 10 × 12 ft | 120 | 11.15 | 13.33 | 132 |
| 12 × 12 ft | 144 | 13.38 | 16 | 159 |
| 12 × 15 ft | 180 | 16.72 | 20 | 198 |
| 14 × 16 ft | 224 | 20.81 | 24.89 | 247 |
| 15 × 20 ft | 300 | 27.87 | 33.33 | 330 |
| 20 × 20 ft | 400 | 37.16 | 44.44 | 440 |
The “with waste” column is rounded up to a whole square foot, since that’s how you’d buy material.
Tips for measuring
- Measure wall to wall at floor level, and round up to the nearest inch.
- Split odd shapes. An L-shaped room is two rectangles. A room with an angled corner is a rectangle plus a triangle, or a trapezoid.
- Leave out what you won’t cover. For flooring, skip areas under built-in cabinets or islands. For paint, measure walls instead: height × width of each wall, minus doors and windows.
- Convert feet and inches first. 11 ft 4 in is 11 + 4 ÷ 12 = 11.33 ft.
- Check the units on the box. Flooring is sold by the square foot or the carton, carpet often by the square yard, and imported products by the square meter.
Square footage of a home
The square footage in a home listing is usually the finished, heated living area, often measured from the outside of the exterior walls, and it may not include garages, unfinished basements or porches. Measuring each room from the inside will give a smaller total because it leaves out wall thickness, closets and hallways you didn’t measure. Builders, appraisers and listing services each have their own measuring rules, so a listing figure is best treated as a guide. If you’re comparing homes by price per square foot, the home affordability calculator and mortgage calculator can help you work out what fits your budget.
Assumptions and limitations
- All shapes are flat and measured horizontally. For a sloped lawn or roof, the true surface is larger than its footprint.
- Areas are added together, never subtracted. To leave out an island or a column, measure around it as separate shapes.
- Waste and cost are applied to the total area. Your supplier may also require buying full cartons or rolls.
- For a slab, patio or footing, you’ll also need the thickness: the concrete calculator turns the area into cubic yards and bags.
Frequently asked questions
How do I calculate square footage?
For a rectangle, multiply the length by the width in feet. A 15 by 12 foot room is 180 square feet. For other shapes, use the matching area formula, and for an L-shaped or irregular space, split it into simple shapes and add their areas together.
How do I calculate the square footage of an L-shaped room?
Split the L into two rectangles that don't overlap, find each area and add them. For example, a 12 by 10 foot section plus an 8 by 6 foot section is 120 + 48 = 168 square feet. Choose 2 areas in the calculator and enter each rectangle.
How do I convert square feet to square meters?
Multiply square feet by 0.09290304, because one foot is exactly 0.3048 meters. So 300 square feet is about 27.87 square meters. To go the other way, multiply square meters by about 10.764.
How many square feet are in a square yard?
Nine, because a yard is 3 feet and 3 × 3 = 9. Divide square feet by 9 to get square yards, so a 12 by 12 foot room is 144 ÷ 9 = 16 square yards. Carpet is often priced per square yard.
How much extra flooring should I buy?
A waste allowance of about 10% is a common starting point for straightforward rooms, and that's the default here. Diagonal layouts, patterned materials and rooms with many corners use more, so allow extra and check the manufacturer's guidance for your product.
How do I measure feet and inches?
Convert the inches to a decimal of a foot by dividing by 12. So 12 feet 6 inches is 12.5 feet and 10 feet 9 inches is 10.75 feet. You can also switch the calculator to inches and enter everything in inches; it converts to square feet for you.
Updated November 2026. Results are estimates for educational purposes and depend on the inputs you provide.