Area can be the known value
For rectangles, circles, sectors, ellipses, trapezoids, parallelograms, rhombuses, regular polygons, annuli, and kites, switch “Solve for” to a dimension and work backward.
MEASURE · REVERSE-SOLVE · COMBINE
Area Calculator
Pick a shape, enter what you know, and solve the area—or work backward from area to a missing dimension.
14 shapescommon + advanced
mixed unitslength + area
visualformula + diagram
SHAPE WORKSPACE
Start with the shape, not the formula.
Live result updates as you type.
RECTANGLE12 m²
A = l × w
COMMON UNITS12 m²
SQUARE FEET129.167 ft²
ACRES0.002965 acres
HECTARES0.0012 ha
COMPOSITE AREA0 m²Add or subtract the current result to build rooms, lots, cutouts, or irregular figures.
Use the information you actually have
Choose base × height, three sides with Heron’s formula, or two sides with the included angle. Invalid side sets are rejected instead of producing fake answers.
Convert at the calculation boundary
Length inputs can use millimetres through miles. Area answers can switch among metric, imperial, acres, hectares, and square miles without re-entering the shape.
Add rooms, subtract cutouts
Save the current shape into a running total. This keeps irregular floor plans and land-area estimates inside one calculator instead of forcing manual arithmetic.
RECENT CALCULATIONS
Reuse a shape without starting over
Saved calculations appear here.
FORMULA REFERENCE
Details stay below the calculator
Quadrilaterals
Rectangle A=lw
Square A=s²
Trapezoid A=½(a+b)h
Parallelogram A=bh
Rhombus A=½d₁d₂
Quadrilateral A=½ef sin θ
Curves
Circle A=πr²
Sector A=½r²θ
Ellipse A=πab
Annulus A=π(R²−r²)
Segment A=½r²(θ−sinθ)
Triangles
Base-height A=½bh
Heron A=√s(s−a)(s−b)(s−c)
SAS A=½ab sin C
Regular polygon
A=ns²/(4 tan(π/n))
Also reports apothem, perimeter, and circumradius.
Conventions, precision & privacy
Units
Each length input converts to metres internally and area converts through square metres. Angle formulas use radians internally even when degrees are selected.
Precision
Results use JavaScript double-precision arithmetic and are displayed with up to 12 significant digits. Derived ellipse circumference uses Ramanujan’s approximation and is labelled as an approximation.
Composite totals
Composite entries preserve the underlying square-metre value so changing the answer unit does not compound rounding error.
Privacy
The calculator runs locally. Recent calculations and composite entries are stored in this browser only.