What this calculator does
Find the size of a floor, patio, lawn or wall in square feet, and what the material for it will cost. Most real spaces aren't perfect rectangles. But almost all of them can be split into a few simple pieces. Use rectangles, triangles for angled corners, and circles for round patios or tree rings. Measure each piece, find its area, and add them up. The calculator does that for up to six sections at once.
You can measure in feet, inches, yards, meters or centimeters. The total also appears in square feet, square meters, square yards and acres. To get you started on flooring, it fills in 10% extra for waste and a price of $3.50 per square foot. Change them to match your quote, or clear the price if you only need the area.
Where it's used
Why this math matters outside the classroom:
- Room size. A 15 × 12 ft bedroom is 180 ft², the number used for flooring, rent comparisons and furniture planning.
- L-shaped spaces. An L-shaped room splits into a 20 × 12 ft rectangle and a 10 × 8 ft rectangle for a total of 320 ft².
- Triangular gardens. A corner bed with legs of 8 ft and 6 ft is a right triangle of 8 × 6 ÷ 2 = 24 ft².
- Circular patios. A round patio 10 ft across covers π × 5² ≈ 78.5 ft².
- Cost estimates. At $4.50 per square foot, 320 ft² of carpet costs $1,440 before installation.
Grade level and standards: Grades 6–7; Common Core State Standards for Mathematics 6.G.A.1, 7.G.B.4. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
How to use it
- Pick the unit you measured in and how many sections make up the space.
- For each section, choose its shape. Enter its length and width, a triangle's base and height, or a circle's diameter. For an L-shaped room, use two rectangles that don't overlap.
- Set the waste percentage and the price per square foot, yard or meter from your quote.
- Read the total area, the cost, the converted areas and the table of sections below the result.
What the inputs mean
- Measurement unit
- Tape measures show feet and inches, but the calculator needs one unit. Turn inches into decimal feet by dividing by 12 (9 in = 0.75 ft). Or switch the unit to inches and enter everything in inches.
- Number of sections
- Split an odd-shaped floor plan into pieces that touch but don't overlap. Counting the same strip twice is the most common mistake.
- Section 1 shape
- Measure a triangle's height straight up from its base, at a right angle, not along the sloping side. For a circle, measure straight across through the center.
- Waste allowance
- Extra for offcuts, matching patterns and mistakes. It raises the area used for the cost, not the measured total.
- Cost per unit area (optional)
- Leave it blank if you only need the area. The price can be per square foot, per square yard (common for carpet) or per square meter.
Formula and method
rectangle area = length × width triangle area = base × height ÷ 2 circle area = π × (diameter ÷ 2)² total area = sum of all section areas area with waste = total area × (1 + waste % ÷ 100) cost = area with waste (in the price's unit) × price per unit area
Area is how much flat surface a shape covers, counted in squares. A rectangle's area is its length times its width. A triangle is half a rectangle, so its area is base times height, halved. For a circle, π (pi) is about 3.14, and the diameter is the distance straight across. The answer is in square units of whatever you measured in, such as square feet. Areas of separate pieces can be added together.
Conversions use exact values: 1 ft = 0.3048 m, so 1 ft² = 0.09290304 m². Also, 1 yd² = 9 ft² and 1 acre = 43,560 ft². The cost uses the area after the waste allowance, because that's how much you'd actually buy.
Worked example
A living room measures 12 ft × 10 ft, and the dining area next to it is 10 ft × 8 ft. Flooring costs $3.50 per square foot, and you want 10% extra for waste.
- Living room: 12 × 10 = 120 ft².
- Dining area: 10 × 8 = 80 ft².
- Total: 120 + 80 = 200 ft².
- With 10% waste: 200 × 1.1 = 220 ft².
- Cost: 220 × $3.50 = $770.00.
Result: The space is 200 ft² (18.58 m²). Buying enough for 220 ft² at $3.50 per square foot comes to about $770.
Understanding the result
The total area is the surface you measured. The area with waste is how much material to buy. It's always the bigger number when the waste percentage is above zero.
The table of sections shows how much each part adds. That helps when different areas get different finishes.
Assumptions and limitations
- Each section is a true rectangle with square corners.
- Sections don't overlap. If they did, the overlap would be counted twice.
- The price is a flat rate per unit of area. No minimum charge, labor or delivery is added.
- Only rectangles, triangles and full circles are built in. For a half circle, enter the full circle and halve the answer. For trapezoids, ovals and other shapes, use the area calculator and add the result.
- The calculator doesn't take out fixed objects such as kitchen islands or built-in cabinets. Leave them out by measuring around them.
- The official square footage in a property listing may follow local measuring rules. Those can differ from adding up floor areas.
Frequently asked questions
How do I measure an L-shaped room?
Draw a line that splits the L into two rectangles. Measure each rectangle's length and width and enter them as two sections. The calculator adds them up. Make sure you count the strip along the dividing line only once.
How do I convert inches to square feet?
Measure in inches and choose inches as the unit. The calculator converts the square inches for you. One square foot is 144 square inches, so 120 in × 96 in = 11,520 in² = 80 ft².
How much waste should I allow?
For flooring laid in straight rows, 5–10% is a common allowance. Diagonal or patterned layouts, rooms with many corners, and materials with a repeating pattern often need 15% or more. Check what the installer or manufacturer recommends.
How do I measure feet and inches for square footage?
Turn the inches into part of a foot by dividing by 12, then multiply as usual. A room 12 ft 6 in by 10 ft 9 in is 12.5 × 10.75 = 134.375 ft². That's about 134.4 square feet.
How much does flooring cost for a 200 square foot room?
Multiply the area you'll buy by the price per square foot. With 10% extra for waste, 200 ft² becomes 220 ft². At $3.50 per ft² for material, that's $770. Installation, underlayment and trim are usually priced separately. If your quote lists them per square foot, add those in too.
Is carpet priced per square foot or per square yard?
Both are used. If your quote is per square yard, choose 'per yd²' next to the price. One square yard is 9 square feet, so $27 per yd² is the same as $3 per ft².
How this calculator is checked
Method: Area of a rectangle (length × width); exact unit definitions (1 ft = 0.3048 m, 1 yd = 3 ft). The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
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