🟦Area Calculator
Pick a shape and enter its dimensions to calculate area, with the formula shown.
Runs entirely in your browser. No data is sent to a server.
Free Area Calculator
Calculate the area of any common shape with our free area calculator. Pick from triangles, rectangles, squares, circles, trapezoids, parallelograms, rhombuses, regular polygons, ellipses, and circular sectors — enter the relevant dimensions, and get the area instantly with the exact formula shown, substituted with your values.
Triangles can be solved from base and height, or from all three sides using Heron's formula. Circles, sectors, and ellipses show results in exact π-form as well as decimal. Regular polygons compute area correctly from either side length or apothem, using the proper trigonometric formula rather than an approximation.
Every input is validated for the shape you've picked, so impossible dimensions (like sides that can't form a triangle) are caught immediately. No sign-up, no downloads — just pick your shape and calculate. See the About page or the FAQ for more.
About the Area Calculator
Supported shapes
Triangle
Base & height, or Heron's formula from 3 sides.
Rectangle & square
l×w or s².
Circle & sector
πr², shown in exact π-form.
Trapezoid & parallelogram
½(b₁+b₂)h and base×height.
Rhombus
½ times the two diagonals.
Regular polygon & ellipse
Trigonometric polygon formula; πab for ellipse.
Validation
Every shape checks for positive dimensions; the 3-side triangle mode additionally checks the triangle inequality before computing an area.
Frequently Asked Questions
Which shapes are supported?
Triangle, rectangle, square, circle, trapezoid, parallelogram, rhombus, regular polygon, ellipse, and circular sector.
How is triangle area calculated?
Either from base and height (½bh), or from all three sides using Heron's formula.
Does it show the formula used?
Yes, each shape shows its formula with your values substituted in.
How is regular polygon area calculated?
Using the formula based on number of sides and side length (or apothem), not an approximation.
Are circle-based results exact?
Yes, shown in π-form (e.g. 25π) alongside the decimal.
What units does it use?
It's unit-agnostic; results are labeled in units² matching whatever unit you entered.
What if my triangle sides are invalid?
The triangle inequality is checked, and invalid combinations are flagged.
Can I calculate a sector's area?
Yes, enter the circle's radius and the sector's central angle.
Is it free?
Completely free, no sign-up or limits.
Does it work on mobile?
Yes, fully responsive.