Online Calculators FreeReference Manual

Geometry Calculator

Every common geometry formula in one tool: areas, volumes, perimeters, diagonals, the Pythagorean theorem, distance and midpoint — pick a shape from the dropdown.

Free toolNo signupFormula shown
Saved & recent
CalculatorFORM GEOMETRY CALCULATOR
Quick set
RESULT
—

One page, every shape

Choose the shape or formula from the dropdown and the form adapts: two fields for a circle, three for Heron's formula, four for the distance between points. Every result shows the substituted formula beneath the board, exactly like the rest of the manual.

The formulas at a glance

Circle A = πr², C = 2πr. Triangle A = ½bh, or Heron's √(s(s−a)(s−b)(s−c)) for three sides. Box V = lwh, S = 2(lw + lh + wh). Sphere V = 4/3πr³, S = 4πr². Cylinder V = πr²h. Cone V = πr²h/3 with slant √(r²+h²). Regular polygon A = ns²/(4 tan(π/n)).

Worked example

  1. A 3-4-5 triangle via the Pythagorean tool.
  2. Enter legs 3 and 4, leave the hypotenuse blank.
  3. c = √(9 + 16) = √25 = 5.
  4. The board also shows area 6 and perimeter 12.

How to use it

  1. Pick the shape or formula from the dropdown.
  2. Fill the fields that appear (leave blanks only where the tool solves for a side).
  3. Read the result and the substituted formula.
  4. Copy, print, or share the link — it remembers the member and your values.

Frequently asked questions

How do I find the area of a circle?

Multiply π by the radius squared: A = πr². With the diameter instead, use A = πd²/4. Both are members of the dropdown.

How do I calculate volume?

Prisms and cylinders multiply base area by height; cones and pyramids take a third of that; spheres use 4/3πr³. Each has its own dropdown member with the formula shown.

What is the Pythagorean theorem?

For a right triangle, a² + b² = c². This page solves for whichever side you leave blank, and checks that the inputs actually form a valid triangle.

Can it solve for a missing side, not just the hypotenuse?

Yes — leave the leg you want blank and fill the other leg plus the hypotenuse. The tool rejects impossible combinations (a leg longer than the hypotenuse).

Does it handle irregular shapes?

For irregular polygons, split the shape into triangles and rectangles, compute each piece, and add. Heron’s formula member handles any triangle from its three sides.

What units does it use?

It is unit-agnostic: the output carries the square or cube of whatever you enter. The margin note above warns about mixing units.