Geometry Calculators
Triangles, circles, plane shapes, solids and coordinate geometry.
Calculators
- Triangle Calculator
Solve a triangle from SSS, SAS, ASA, AAS or SSA, including the ambiguous case.
- Circle Calculator
Radius, diameter, circumference and area from any one of them.
- Area and Perimeter Calculator
Rectangle, square, parallelogram, trapezoid and ellipse area and perimeter.
- Volume and Surface Area Calculator
Cube, cuboid, cylinder, sphere, cone and pyramid volume and surface area.
- Slope, Distance and Midpoint Calculator
Slope, line equation, distance and midpoint between two points.
Choosing a geometry calculator
Choose by the shape and by what you already know. Each calculator takes the measurements you have and works out the rest, with the formula and units shown.
- A triangle with some sides and angles known?
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Solves from three sides, two sides and an angle, or two angles and a side, and shows both answers when the measurements allow two different triangles.
- Anything about a circle?
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Enter one of radius, diameter, circumference or area to get the other three, exactly in terms of π and as decimals.
- Floor area or fence length?
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Area and perimeter of rectangles, squares, parallelograms, trapezoids and ellipses.
- How much a solid holds, or how much covers it?
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Volume and Surface Area Calculator
Volume and surface area of cubes, boxes, cylinders, spheres, cones and pyramids.
- Two points on a graph?
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Slope, Distance and Midpoint Calculator
Slope, distance, midpoint and the equation of the line through them.
Have these to hand
- Every measurement in one unit, or the unit of each noted.
- For a triangle, which angle sits between which two sides.
Mistakes that change the answer
- Mixing units, such as feet for the length and inches for the width.
- Scaling areas like lengths. A square foot is 144 square inches, not 12.
- Entering the diameter where the formula asks for the radius.
- Trusting a sketch over the numbers; the answer follows the measurements, not the drawing.
Related guides
- How to measure a room for square footage and volume
Measure, convert inches to decimal feet, split odd shapes into rectangles, then multiply and convert with a squared or cubed factor. Worked with an L-shaped room, a concrete pad and a water tank.
- Solving triangles: which rule to use, and the SSA ambiguous case
A table for choosing the law of sines or the law of cosines, a worked SSA example with two valid answers, and the step-order and rounding traps that make hand-solved triangles go wrong.
- How much extra flooring, tile, paint and concrete to buy
Published rules of thumb for overage by material and layout, what each one covers, and worked examples that apply the allowance first and round up to whole boxes, cans and bags last.
- Unit conversion pitfalls: gallons, tons, cups, GB vs. GiB
Nine unit traps with the numbers worked out: US vs. imperial gallons and pints, fluid ounces vs. ounces, three kinds of ton, cups of flour in grams, cup and tablespoon sizes, GB vs. GiB, bits vs. bytes, temperature changes and UK vs. US mpg.
- Mean, median or mode? How to choose a summary statistic
How to pick the center and spread that describe your data fairly, with worked numbers and a side-by-side of the quartile rules that different tools use.
- Common percentage mistakes and how to avoid them
Six percentage slips that produce confident wrong answers, from percentage points to negative starting values, each worked with example numbers you can check.