Geometry

Geometry tools solve the shape questions that show up in homework, DIY and site work: triangles, circles, area, volume and surface area.

Pick one length unit and the page keeps area (unit²) and volume (unit³) distinct so sides and volumes are never mixed. a² + b² = c² applies only when one angle is 90° — the Pythagorean guide covers the converse and the triples that are not a spell.

Open a triangle page when you have three mixed facts (SSS, SAS, ASA) rather than two legs of a right triangle.

Featured in this category

Triangle Calculator
Find a triangle’s area, perimeter and angles from three sides, or the area from base and height or SAS.
Area Calculator
Find the area of a square, rectangle, triangle, circle, trapezoid, parallelogram or ellipse.
Pythagorean Theorem
Find the hypotenuse from two legs, or a missing leg from the hypotenuse and the other leg.

Guides

How the Pythagorean Theorem Works
On a right triangle, the square of the hypotenuse equals the sum of the squares of the two legs. That identity finds a missing side. It does not apply to an acute or obtuse triangle unless you already know the right angle.

2D Geometry

Area Calculator
Find the area of a square, rectangle, triangle, circle, trapezoid, parallelogram or ellipse.
Circle Calculator
From radius, diameter or circumference, get the other two plus the area of a circle.
Slope Calculator
Find the slope of a line from two points or from rise and run, plus the angle from the positive x-axis.

3D Geometry

Volume Calculator
Find the volume of a cube, box, sphere, cylinder, cone or rectangular pyramid in unit³.
Surface Area
Find the total surface area of a cube, box, sphere, cylinder or cone, including slant height for a cone.

Triangles & Distance

Triangle Calculator
Find a triangle’s area, perimeter and angles from three sides, or the area from base and height or SAS.
Right Triangle
From two legs, or a leg and the hypotenuse, get the third side, both acute angles, area and perimeter.
Pythagorean Theorem
Find the hypotenuse from two legs, or a missing leg from the hypotenuse and the other leg.
Distance Calculator
Find the straight-line distance between two points in a plane or in 3-D space.

All geometry tools

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9 tools

Triangle Calculator
Find a triangle’s area, perimeter and angles from three sides, or the area from base and height or SAS.
Volume Calculator
Find the volume of a cube, box, sphere, cylinder, cone or rectangular pyramid in unit³.
Slope Calculator
Find the slope of a line from two points or from rise and run, plus the angle from the positive x-axis.
Area Calculator
Find the area of a square, rectangle, triangle, circle, trapezoid, parallelogram or ellipse.
Distance Calculator
Find the straight-line distance between two points in a plane or in 3-D space.
Circle Calculator
From radius, diameter or circumference, get the other two plus the area of a circle.
Surface Area
Find the total surface area of a cube, box, sphere, cylinder or cone, including slant height for a cone.
Pythagorean Theorem
Find the hypotenuse from two legs, or a missing leg from the hypotenuse and the other leg.
Right Triangle
From two legs, or a leg and the hypotenuse, get the third side, both acute angles, area and perimeter.