Geometry Calculator
A free online geometry calculator for solving triangles, quadrilaterals and polygons, coordinate geometry, parallel-line transversal angles, and circle & solid geometry. Enter what you know, and it shows the governing formula alongside the answer — a fast geometry problem solver for homework, teaching, or a quick check.
What This Geometry Calculator Solves
Five focused modes cover the geometry problems that come up most in algebra, geometry class, and coordinate geometry — each one shows the formula it used, not just the final number.
- Solve a triangle from SSS, SAS, ASA, AAS, or right-triangle legs
- Identify the congruence postulate (SSS, SAS, ASA, AAS, HL)
- Check if two triangles are similar or congruent
- Find missing polygon and quadrilateral angles
- Solve a parallelogram or isosceles trapezoid
- Distance, midpoint, and slope between two points
- Area and perimeter of a polygon from its vertices
- Check if a quadrilateral is a parallelogram from coordinates
- Label all 8 angles from a parallel-line transversal
- Circle, inscribed circle, and 3D solid measurements
Formula Reference
| Concept | Formula |
|---|---|
| Pythagorean Theorem | a² + b² = c² |
| Law of Cosines | c² = a² + b² − 2ab·cos(C) |
| Law of Sines | a / sin(A) = b / sin(B) = c / sin(C) |
| Heron's Formula | Area = √(s(s−a)(s−b)(s−c)), where s = (a+b+c)/2 |
| Polygon Interior Angle Sum | (n − 2) × 180° |
| Regular Polygon Interior Angle | (n − 2) × 180° / n |
| Circle Area / Circumference | A = πr² C = 2πr |
| Distance Formula | d = √((x₂−x₁)² + (y₂−y₁)²) |
| Midpoint Formula | M = ((x₁+x₂)/2, (y₁+y₂)/2) |
| Slope Formula | m = (y₂−y₁) / (x₂−x₁) |
| Shoelace Formula (polygon area) | Area = ½ |Σ(xᵢyᵢ₊₁ − xᵢ₊₁yᵢ)| |
| 3D Pythagorean Theorem (space diagonal) | d = √(l² + w² + h²) |
How To Use The Geometry Calculator
Pick the mode that matches your problem. Triangle mode covers SSS, SAS, ASA, AAS, and right triangles. Quadrilateral & Polygon covers angle sums, parallelograms, and trapezoids. Coordinate Geometry works from x,y points. Parallel Lines covers transversal angle relationships. Circle & Solids covers circles, inscribed circles, and 3D shapes.
- Choose a mode from the row above the calculator.
- Enter the values you already know into the matching fields.
- Press the calculate button for that panel.
- Read the result panel — it lists every value found, along with the formula or postulate used.
Quick Action Steps
- Pick a mode: Triangle, Quadrilateral & Polygon, Coordinate, Parallel Lines, or Circle & Solids.
- Fill in the known values for that specific tool.
- Press Calculate and read the labeled results below it.
⚠ Watch Out For This
A set of three side lengths that doesn't satisfy the triangle inequality (any two sides must add up to more than the third) cannot form a real triangle, and the SSS solver will flag it as invalid rather than return an answer.
How This Compares To Other Geometry Tools
Desmos Geometry, Symbolab's geometry calculator, Mathway's geometry solver, and MathPapa are all established tools for geometry help, and a TI-84 or TI-Nspire can handle plenty of this with the right app. AceCalculator's geometry calculator exists for the moments you want a specific triangle, angle, or coordinate answer fast, without opening a separate platform.
- ✓ No download, install, or account, unlike a TI-84 app or a Mathway sign-in
- ✓ Five focused modes — Triangle, Quadrilateral & Polygon, Coordinate, Parallel Lines, Circle & Solids — in one page
- ✓ States the formula or congruence postulate behind every answer
- ✓ Checks triangle similarity, congruence, and quadrilateral-from-coordinates classification
- ✓ Runs entirely in your browser; nothing is stored or sent to a server
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Content Researcher · AceCalculator
Amanda Reeds researches and builds AceCalculator's math tools, with a focus on matching each calculator's output to standard classroom notation. She has written and verified the working behind AceCalculator's algebra, graphing, and equation-solving calculators.
Frequently Asked Questions
Yes. Every mode — triangles, quadrilaterals and polygons, coordinate geometry, parallel lines and transversals, and circles and solids — is free, with no account, signup, or download required.
It solves triangles from three known sides or angles (SSS, SAS, ASA, AAS, or right-triangle legs), finds missing quadrilateral and polygon angles, works out distance, midpoint, slope and area from coordinates, labels every angle formed by a transversal crossing two parallel lines, and finds circle, inscribed-circle, and 3D solid measurements.
Yes. Enter the three side lengths and the Law of Cosines is used to find all three angles, plus the area, perimeter, and triangle classification (equilateral, isosceles, or scalene; acute, right, or obtuse).
Yes. Based on which three values you enter (three sides, two sides and the included angle, two angles and the included side, two angles and a non-included side, or two legs of a right triangle), the calculator states whether SSS, SAS, ASA, AAS, or HL applies.
No. It solves for missing sides, angles, and areas and names the theorem or postulate that justifies the result, but it does not generate a full statement-and-reason two-column proof.
Yes. Enter four vertex coordinates in the Coordinate Geometry mode and the calculator checks whether the diagonals bisect each other, then classifies the shape as a parallelogram, rectangle, rhombus, square, or trapezoid based on side lengths and angles.
Pick the position of the one angle you know (1 through 8) in the Parallel Lines mode, enter its degree measure, and the calculator returns all eight angles labeled by relationship: corresponding, alternate interior, alternate exterior, co-interior, vertical, or linear pair.
Yes. Enter a list of vertex coordinates in order in Coordinate Geometry mode and the Shoelace Formula returns the exact area and perimeter of the polygon.
Yes. The Circle & Solids mode calculates a circle's area and circumference from any one known value, and finds the inscribed and circumscribed circle radius of a triangle from its three side lengths.
Yes. Cubes, rectangular prisms, cylinders, cones, and spheres are all supported, including the rectangular prism's space diagonal, which is found with the 3D Pythagorean theorem.
It covers the same core job as Desmos Geometry, Mathway's geometry solver, Symbolab's geometry calculator, and MathPapa: entering known values and getting the missing measurements back. It's a separate, independent tool built by AceCalculator, not affiliated with any of them.
Important Disclaimer
AceCalculator's geometry calculator is provided for informational and educational purposes only. It solves for missing measurements and names the applicable formula or postulate, but it does not generate full two-column geometric proofs. It is an independent tool and is not affiliated with, endorsed by, or a product of Desmos, Symbolab, Mathway, MathPapa, or Texas Instruments. Results are for reference and are not a substitute for verification by a qualified instructor where accuracy is critical. See our full Disclaimer and Terms and Conditions.