👆 Drag to Rotate • 📜 Scroll/Pinch to Zoom • Right-click to Pan
🛠️ Drawing Tools
📐 Classical Constructions
🔵 Conic Sections
📏 Measurement Calculator
Select two points, then click calculate:
🔺 Triangle Centers
Select a triangle to calculate centers:
📚 Learning Resources
✏️ Annotations
🔄 Transform
🖥️ Display Settings
⬡ Polygon Settings
Sides:6
0 shapes • 100% • 0, 0
💡 Tips: Shift+Click to multi-select • R to rotate • M to mirror
Space+Drag to pan • Scroll to zoom • Esc to cancel
3D ModeSelect Tool
🔋 100%Light
Keyboard Shortcuts
Undo
Ctrl + Z
Redo
Ctrl + Y
Select All
Ctrl + A
Deselect
Esc
Delete
Del
Zoom In
+
Zoom Out
-
Reset View
0
Copy
Ctrl + C
Paste
Ctrl + V
Pan Mode
Space + Drag
Tool Shortcuts
S/P/L/R/C/T/G
Arc / Ellipse
A / E
Spline / Text
B / X
Dim / Angle
D / N
Compass / Bezier
O / V
Perp Bisector / Angle Bisector
J / K
Parallel / Perpendicular
Q / W
Rotate 45°
R
Mirror Horizontal
Shift + M
Toggle Grid/Axes
G / F
Triangle Centers
Select a triangle and click "Calculate Centers"
📏 Measurement Calculator
Select two points, then calculate:
🎓 Geometry Tutorial
Getting Started
Welcome to the Calc84 Geometry Calculator! This tool provides classical compass and straightedge constructions along with modern geometric analysis.
Select Tool (S): Click and drag to select shapes
Point Tool (P): Place single points on the canvas
Line Tool (L): Draw straight lines
Compass Tool (O): Classical compass constructions
Classical Constructions
Use our Cabri Jr.-style tools for geometric constructions:
Perpendicular Bisector: Select two points to create the perpendicular bisector
Angle Bisector: Select vertex and two points on the angle rays
Parallel Line: Select a line, then a point to draw through
Perpendicular Line: Select a line, then a point for perpendicular
Triangle Centers
Create a triangle, then click "Calculate Centers" to discover:
Centroid (G): Intersection of medians
Circumcenter (O): Center of circumscribed circle
Incenter (I): Center of inscribed circle
Orthocenter (H): Intersection of altitudes
📚 Geometry Formula Reference
Coordinate Geometry
Distance Formulad = √[(x2-x1)² + (y2-y1)²]
Midpoint FormulaM = ((x1+x2)/2, (y1+y2)/2)
Slopem = (y2-y1)/(x2-x1)
Line Equationy = mx + b
Circle
AreaA = πr²
CircumferenceC = 2πr
Triangle
AreaA = ½bh
CentroidG = ((x1+x2+x3)/3, (y1+y2+y3)/3)
Pythagorean Theorema² + b² = c²
Conic Sections
Parabolay = a(x-h)² + k
Ellipse AreaA = πab
Hyperbola(x-h)²/a² - (y-k)²/b² = 1
Free Online Geometry Calculator
Free online geometry workspace — draw and measure 2D figures with compass-and-straightedge construction tools, find a triangle's centroid, circumcenter, incenter, and orthocenter, and plot 3D surfaces as z = f(x,y). Selecting a shape shows its area, perimeter, side lengths, or slope in the properties panel. Includes a built-in formula reference. No download, runs in any browser.
A Single Workspace for 2D Constructions and 3D Surface Plotting
This tool has two modes. The 2D Plane is a construction canvas: you draw points, lines, rectangles, circles, arcs, ellipses, triangles, polygons, splines, and Bezier curves, then build on them with classical compass-and-straightedge tools such as the compass, perpendicular bisector, angle bisector, parallel line, and perpendicular line. The 3D Grapher plots a surface described as a function of two variables, z = f(x,y), as a parametric definition, or as a scatter plot of points read from lists. There is no dimension-entry form to fill in — what you draw is what gets measured, and each shape's numbers appear in the properties panel when you select it.
Select a shape you have drawn and the properties panel reads it back to you — area and perimeter for rectangles, triangles, and polygons; area for ellipses; radius, diameter, and circumference for circles; length, angle, and slope for lines. The Measurement Calculator works on two selected points and returns the distance, midpoint, slope, and line equation, while the Triangle Centers button computes the centroid, circumcenter, incenter, and orthocenter of a selected triangle. Clicking Cheat Sheet opens a short formula reference for coordinate, circle, triangle, and conic formulas.
A Quick Tour of the Geometry Workspace: Shapes, Constructions, and 3D Views
If you have never used an online geometry tool before, here is the fastest way to get started:
Switch to the 2D Plane. Click the 2D Plane tab, then pick a drawing tool: point, line, rectangle, circle, arc, ellipse, triangle, polygon, regular polygon, spline, or Bezier.
Draw on the canvas. Click to place a point or a vertex, and drag to size a shape. Shift+click adds to the selection, Space+drag pans, the scroll wheel zooms, and Esc finishes or cancels the shape you are drawing.
Read the measurements. Click a shape to select it and the properties panel lists its numbers — area, perimeter, side lengths, radius, slope, and more. Nothing has to be typed in first.
Build a construction. Use the classical tools — compass, perpendicular bisector, angle bisector, parallel line, or perpendicular line — on the shapes you have drawn. Select a triangle and press Calculate Centers to find its centroid, circumcenter, incenter, and orthocenter.
Explore 3D surfaces. Switch to 3D Grapher mode and enter a function like sin(x) + cos(y). Drag to rotate, scroll to zoom, toggle the wireframe, and use the plane slicer to place a translucent cutting plane through the surface.
The Full Feature Set: 2D Drawing, Constructions, Measurement, and Surface Plotting
2D drawing tools — point, line, rectangle, circle, arc, ellipse, triangle, polygon, regular polygon (3 to 12 sides), spline, and Bezier curve
Properties panel — select a shape to read its measurements: area and perimeter for rectangles, triangles, and polygons; area for ellipses; radius, diameter, and circumference for circles; length, angle, and slope for lines
Classical constructions — compass, perpendicular bisector, angle bisector, parallel line, and perpendicular line
Measurement calculator — select two points to get the distance, midpoint, slope, and line equation
Triangle centers — centroid, circumcenter, incenter, and orthocenter for a selected triangle
Conic sections — parabola (vertex, focus, direction) and hyperbola (center, a, b, c)
3D surface grapher — plot z = f(x,y), parametric surfaces, and 3D scatter plots from lists, with mesh density, wireframe toggle, auto-rotate, and a plane slicer on the X, Y, or Z axis
Built-in formula reference — a cheat sheet of coordinate, circle, triangle, and conic formulas
Keyboard shortcuts — S (select), P (point), L (line), R (rectangle), C (circle), T (triangle), G (polygon) and more
Runs in any browser — reliable on Chromebooks during exams and in classrooms with spotty WiFi
Calc84 geometry calculator — 3D surface plots and 2D geometric constructions in one workspace.
How Do I Find the Centroid of a Triangle? — Worked Example
Say you have a right triangle with vertices at A(0, 0), B(6, 0), and C(0, 3). Draw it with the Triangle tool, or place three points and connect them. Select the triangle and click Calculate Centers. The centroid is the average of the three vertices: G = ((0 + 6 + 0)/3, (0 + 0 + 3)/3) = (2, 1). The same panel reports the other three centers and draws them on the canvas: the circumcenter lands at (3, 1.5), the midpoint of the hypotenuse, which is exactly where the circumscribed circle's center belongs in a right triangle; the orthocenter coincides with the right-angle vertex at (0, 0); and the incenter sits at approximately (1.15, 1.15), one inradius in from each leg. Seeing all four land where the theorems predict is a much better check on your understanding than reading the definitions.
For students moving into calculus, seeing a surface as a whole is the groundwork for thinking about solids. The 3D Grapher draws z = f(x,y) as a lit, shaded mesh you can rotate, zoom, and switch to wireframe, and the plane slicer places a translucent cutting plane through the surface at a value you choose along the X, Y, or Z axis — the same "hold one variable fixed" move that sets up a cross-section argument. Hover over the mesh and a trace readout reports the (x, y, z) coordinates of the nearest plotted point.
Which Shapes Can You Draw, and What Does Each One Report?
The canvas covers the figures that come up in high school and introductory college geometry. Straight-line tools are point, line, rectangle, triangle, and polygon; curved tools are circle, arc, ellipse, spline, and Bezier curve; regular polygons take a side count from 3 to 12; and conic sections add the parabola (vertex, focus, direction) and hyperbola (center, a, b, c). Selecting any of them reports its measurements in the properties panel.
Because every measurement comes from a shape you drew rather than a number you typed, the workflow matches how geometry is usually taught: construct the figure, then read what is true about it. The construction tools are useful for demonstrating classical proofs and transformations visually, and the formula cheat sheet is there when you need to check a definition rather than a number.
Common Questions About the 2D Canvas and 3D Grapher
Is this geometry calculator free?
Yes, completely free. Every tool — the 2D drawing and construction tools, the measurement calculator, the triangle centers, and the 3D grapher — works without signup, download, or payment. There is no limit on how many shapes you can draw, and no feature is held back behind a paywall.
Does it show the formula used for each calculation?
No. The properties panel reports the measured values — area, perimeter, side lengths, radius, slope, and so on — but it does not print the formula or a substitution step. For the formula itself, open the Cheat Sheet panel, which lists the coordinate, circle, triangle, and conic formulas. The worked example above shows the arithmetic done by hand.
Can it calculate 3D shapes like cylinders and spheres?
No. The 3D Grapher plots a surface you describe as a function — z = f(x,y), a parametric surface, or a scatter plot from lists — and it has no volume or surface-area formulas for named solids. To see a cylinder's shape, for instance, you would enter its parametric equations and rotate the result; to get its volume you would apply V = πr²h separately.
What is the difference between the 2D Plane and 3D Grapher modes?
The 2D Plane mode is a construction canvas — you draw shapes (points, lines, circles, polygons) with drawing tools and measure distances, angles, and areas. The 3D Grapher mode plots mathematical surfaces like z = sin(x) + cos(y) and lets you rotate, zoom, and place a cutting plane through them. Use 2D for geometry constructions and measurement; use 3D for visualizing multivariable functions and surfaces.
Does it include a Pythagorean theorem calculator?
No. There is no side solver that takes two sides of a right triangle and returns the third. The Pythagorean theorem appears in the Cheat Sheet panel as a reference formula (a² + b² = c²), and you apply it most often through the Distance calculation: select the two endpoints of a segment, run Distance, and the result is the hypotenuse directly.
Can I use this on a phone or tablet?
Yes. The workspace is fully responsive, and the controls panel collapses to a toggle on narrow screens. On touchscreens you can tap to place points and pinch to zoom the canvas, and the same drawing, construction, measurement, and 3D tools are available on mobile and desktop.
Miqdad is a full-stack engineer and cybersecurity student specializing in educational technology (EdTech). He built Calc84's geometry tool to give students a free, interactive way to explore constructions and 3D surfaces.
TI-84 Plus CE is a trademark of Texas Instruments Incorporated. Calc84 is an independent educational project by Miqdad Qaisrani, not affiliated with or endorsed by Texas Instruments. Full disclaimer.
