Geometry calculator for every shape you measure
Area, perimeter, volume, surface area, triangles, slope, distance and midpoint — each with a to-scale diagram and the working shown with your numbers. For homework at the kitchen table or a tape measure in an empty room.
All calculators
Flat shapes
Solids
Triangles
Coordinate geometry
Describe the problem, get the method
Paste a homework question or describe your project. The AI tutor names the formula and works it through step by step. Always check the result with the calculator above.
See why a² + b² = c²
Build a square on each side of a right triangle. Change the legs and watch the two smaller squares always add up to exactly the big one. That is the whole theorem: it's a statement about areas.
9 + 16 = 25 → c = √25 = 5
Whole-number answer: (3, 4, 5) is a Pythagorean triple.
Understand it, don't just compute it
Every formula on this site comes with its reason. Drag the triangle above and the areas of the three squares show why a² + b² = c²; slice a circle on the circle page to see where πr² comes from; pour cones into a cylinder on the cone page to see the one-third. ahaboo carries the same idea further, letting you drag, zoom, and adjust your way through why the Moon has phases, how photosynthesis works, and how tax brackets add up.
What the numbers mean
- Length (ft, m) measures one direction — perimeter, circumference, distance.
- Area (ft², m²) counts unit squares — floors, walls, land, paint coverage.
- Volume (ft³, m³, gallons) counts unit cubes — concrete, water, soil, storage.
Double every length of a shape and its area grows 4×, its volume 8×. That scaling rule is why a 16-inch pizza has more than twice the pizza of a 10-inch one.
Questions people ask
Is CalcShapes free?
Yes. Every calculator is free, runs in your browser and needs no account.
How accurate are the results?
Calculations use full double-precision arithmetic and exact formulas; the display rounds to a sensible number of digits. The ellipse perimeter uses Ramanujan's approximation, which is off by far less than 0.01% for ordinary ovals.
Can I use it for homework?
Yes — every calculator shows the formula and the substitution steps so you can follow and check the method, not just copy the answer.
Which units are supported?
Millimeters to miles for length, with results converted to square feet, square meters, acres, hectares, cubic yards, liters and US gallons where it makes sense.