Calculate area, perimeter, and diagonals for 10 shapes with live SVG visualization and unit selection.
Rectangle
Frequently asked questions
How does the unit selector work?
Choose a unit once and enter all dimensions in that unit. The calculator reports area in that unit squared (for example, cm gives cm²) and perimeter in the same linear unit. Switching unit after typing keeps the numbers you entered and recalculates the result in the new unit.
Which triangle method should I use?
Use Base & height when you know one side and the perpendicular height to it. Use Heron (3 sides) when you know all three side lengths. Use Two sides & angle (SAS) when you know two sides and the included angle in degrees.
What is apothem for a regular polygon?
The apothem is the perpendicular distance from the centre of a regular polygon to the midpoint of any side. It equals s / (2 · tan(π/n)), where s is the side length and n is the number of sides. Area equals half the perimeter times the apothem.
How is the ellipse perimeter computed?
An exact formula for ellipse perimeter requires an integral. This calculator uses Ramanujan's second approximation, π·(a+b)·(1 + 3h/(10+√(4−3h))) with h = ((a−b)/(a+b))². Error is below 0.001% for typical eccentricities.
Can I enter dimensions in mixed units?
No — pick one unit and enter every dimension in it. If your inputs are in different units, convert them first (for example, inches to feet) and then enter the converted values.
Does the sector accept radians or degrees?
Degrees. Enter the central angle from 0 to 360. The calculator converts to radians internally for arc length (L = r·θ) and sector area (A = ½·r²·θ).
Geometry Calculator computes area and perimeter (plus diagonal or apothem where applicable) for ten 2D shapes: rectangle, square, triangle, circle, ellipse, trapezoid, parallelogram, rhombus, regular polygon, and circular sector. For triangles it supports three input methods: base and height, Heron’s formula with three sides, and two sides plus included angle (SAS). A single unit selector (m, cm, mm, ft, in, yd) applies to all dimensions; results use that unit squared for area and the same unit for linear measures. Each shape renders an SVG diagram with labeled dimensions. Example 1: a 20 by 12 cm rectangle gives area 240 cm², perimeter 64 cm, diagonal 23.32 cm. Example 2: a regular hexagon with side 10 cm gives area 259.81 cm² and perimeter 60 cm. The calculator validates positive inputs, enforces the triangle inequality, and uses Ramanujan’s approximation for ellipse perimeter.