Area Calculator
Calculate, understand, and apply area formulas for common shapes. Use the tool below for instant results, then read the guides for geometry, construction, land measurement, and classroom work.
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Area Calculator
Shape selection, dimension inputs, and instant area output. Use one unit per calculation; the result is that unit squared.
Area
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square units (same unit as your inputs, squared)
Choose a shape, enter dimensions, then calculate.
Using this calculator
- Pick the shape that matches your diagram or problem statement.
- Type each dimension using the same unit throughout (meters, feet, inches, and so on).
- Press Calculate area to see the result in square units.
- Switch shapes anytime; fields update automatically for the new figure.
Example calculations
- Rectangle: 10 × 6 → 60 square units
- Triangle: base 8, height 5 → 20 square units
- Circle: radius 4 → about 50.27 square units
What Is Area?
Definition, surface measurement, units, and where area shows up in real projects.
Area tells you how much flat surface a shape covers. Picture counting equal-sized squares that fit inside a boundary without gaps: the count is area, and the square size sets your unit.
A rectangle that is 5 meters long and 4 meters wide covers 20 square meters because 5 rows of 4 unit squares fill the shape. That idea scales to rooms, fields, plates, and any drawn figure once you pick the right formula.
Area differs from length (one dimension) and from volume (three dimensions). For this site we focus on flat figures you can sketch on paper or measure on a plan.
- Definition: the amount of surface inside a closed boundary
- Meaning: how much space a shape occupies in two dimensions
- Units: square meters (m²), square feet (ft²), acres, hectares, and other square-unit names
- Applications: flooring, paint coverage, land parcels, metal sheets, garden beds, and geometry classwork
Area Formula
Pick the relationship that matches your shape before you enter numbers in the tool above.
Most homework and job-site questions use a small set of patterns. The core rectangle rule is A = l × w (area equals length times width). A square is the special case where both sides are equal, so A = s².
Triangles use base and perpendicular height: A = ½ × b × h. Circles use radius: A = πr². Other polygons and composite layouts build on these ideas or split the figure into pieces.
Read more in our area formula guide when you need a formula selection checklist.
Rectangle area formula
A = l × w when sides meet at right angles and you measure the correct pair of edges.
Square area formula
A = s × s = s² where s is the side length.
Triangle area formula
A = ½ × b × h with h perpendicular to the base b. Three-side cases can use Heron's formula (see our triangle area article).
Circle area formula
A = πr². If you know diameter d, radius is d ÷ 2 before you square.
Formula selection guide
- Name the shape or break a complex outline into rectangles and triangles
- List every length you measured and keep one unit system
- Match the shape name to the calculator mode at the top of this page
- Square the unit in the answer (ft becomes ft²)
How to Calculate Area
A repeatable method that works on paper or in the browser tool.
Step one: identify the shape. Step two: measure each required dimension with the same tape or ruler unit. Step three: choose the formula (or calculator mode). Step four: multiply and label the result with square units.
For unit conversion, convert every length before you multiply, then the area carries the squared converted unit. Example: 10 ft × 12 ft = 120 ft². To express that in m², convert feet to meters first or convert the final area using 1 ft² ≈ 0.092903 m².
Our how to calculate area walkthrough expands each step with homework and construction notes.
- Measure dimensions: record base, height, radius, or side lengths clearly on a sketch
- Select the correct formula: align with the shape list in the calculator
- Calculate area: run the math by hand or press Calculate area in the tool
- Unit conversion: convert inputs together, or convert the finished square-unit value once
Area Examples
Sample values you can type into the calculator to verify your own work.
Each card below states the mode to choose in the shape dropdown. Results assume consistent units and the standard formulas built into this page.
Rectangle
Length 12 ft, width 9 ft → area 108 ft². Select Rectangle in the tool.
Square
Side 7 m → area 49 m². Use Rectangle and enter the same value for length and width.
Triangle
Base 10 in, height 6 in → area 30 in². Select Triangle.
Circle
Radius 3.5 m → area about 38.485 m². Select Circle.
Real-world floor plan
A 4.2 m by 3.8 m room is 15.96 m² of floor area before subtracting fixed cabinets you do not cover.
Rectangle Area Calculator
Length and width drive most layout, flooring, and sheet-goods estimates.
Enter length and width in the calculator with shape Rectangle. The tool multiplies them and reports square units automatically.
Construction crews use the same math for carpet pads, plywood sheets, and countertop slabs. Students use it for grid models and scale drawings.
See the dedicated rectangle area calculator article for unit conversion tables and worked homework.
Triangle Area Calculator
Base and perpendicular height cover most textbook and drafting cases.
Choose Triangle, type base and height, then calculate. Height must meet the base at a right angle in the diagram you were given.
When you only know three sides, Heron's formula is the manual path; our blog post explains when to use it versus base-height.
Read triangle area calculator for right-triangle shortcuts and geometry class tips.
Circle Area Calculator
Radius is the fastest input; diameter is easy to halve first.
Select Circle and enter radius. The page uses πr² with π as a standard floating value, then rounds for display.
Engineering sketches often label diameter. Divide by 2 to get radius before calculating, or halve mentally and square the radius as usual.
Visit circle area calculator for irrigation, pipe cross-section, and gear face examples.
Area Unit Converter
Convert square units once you know the area, or convert each length before multiplying.
This calculator outputs area in the square of whatever length unit you typed. Convert inputs first when mixing metric and imperial on one job.
Common conversions on finished area: 1 ft² ≈ 0.092903 m²; 1 m² ≈ 10.7639 ft²; 1 acre = 43,560 ft²; 1 hectare = 10,000 m².
Detailed conversion practice lives in area unit converter.
- Square feet to square meters: multiply ft² by 0.092903
- Acres to square feet: multiply acres by 43,560
- Hectares to acres: multiply hectares by about 2.47105
- Square inches to square feet: divide in² by 144
Area Calculator
The interactive tool at the top of this page is your primary workspace.
Shape selection changes the input fields instantly. Sixteen modes cover rectangles through regular polygons, plus rings and cyclic quadrilaterals.
Nothing you type is uploaded. Results appear in square units derived from your entries, and you can reset or switch shapes without reloading.
For a focused tour, read how this area calculator works.
- Shape selection dropdown
- Dimension inputs that adapt to the figure
- Instant area output with clear error messages
- Example values listed inside the tool panel
Common Area Calculation Mistakes
Mixing units (feet with inches) without converting first is the most common error. Convert every length, then multiply.
Using slant height instead of perpendicular height on triangles and parallelograms inflates area. Height must meet the base at a right angle unless a different definition is stated in your textbook.
Treating diameter as radius for circles doubles the error because area depends on r², not d² directly.
For land and flooring, forgetting to subtract areas you will not cover (stairs openings, islands) leads to over-ordering material.
Area vs Perimeter
Two different questions: how much surface inside versus how far around the edge.
Area uses square units and answers how much space a shape covers. Perimeter (or circumference for circles) uses single units and answers how far you travel along the boundary.
A long skinny rectangle can have a modest area but a large perimeter. Comparing the two measures helps when you fence a yard (perimeter) but seed the lawn (area).
Our area vs perimeter article walks through classroom comparisons without jumping into advanced topics.
FAQs About Area
- What is the main area formula?
- For rectangles, A = l × w (length times width). Other shapes use different relationships; pick the matching mode in the calculator.
- Do I need the same unit for every input?
- Yes. Enter all lengths in one unit (all feet, all meters, etc.). The tool returns square units based on that choice.
- Can this help with construction or land measurement?
- Yes, for flat areas such as floors, roofs, and parcel plans. Always confirm critical measurements in the field and account for waste factors separately.
- How is area different from perimeter?
- Area measures surface inside a shape in square units. Perimeter measures distance around the edge in single units. See the area vs perimeter section above.
- Does the calculator convert square feet to square meters?
- It computes in the square of your input unit. Convert lengths before calculating, or multiply the finished area by a conversion factor. The unit converter section lists common factors.
- Is my data stored?
- No. All math runs locally in your browser on this static page.