Online Student ToolsMeasurement & geometry tools
Online Geometry Compass
Click to place the compass center, then drag outward to draw a circle, just like a real geometry compass. Works with mouse, touch, or stylus.
Showing arbitrary units. Calibrate the ruler to draw in real centimeters or inches.
Click the canvas to place the compass center.
What is a geometry compass?
A geometry compass, also called a drafting or drawing compass, is a two-legged tool used to draw circles and arcs. One leg holds a needle point that stays fixed at the circle's center, while the other holds a pencil at a set distance, the radius. Rotating the compass around the fixed point traces a perfect circle. This tool is an online compass built specifically for that purpose, not a magnetic or directional compass.
How to draw a circle with a compass
Set the needle point at your chosen center. Adjust the opening between the two legs to match your desired radius. Keeping the needle point still, rotate the pencil leg a full turn around it. On this tool, that's a click for the center and a drag for the radius, or an exact radius entered directly if you know the measurement you need.
Finding the radius and diameter of a circle
The radius is the distance from the center to the edge of a circle; the diameter is twice that, the distance all the way across through the center. If you're given a diameter and need to set the compass, halve it first. Every circle drawn with this tool shows its radius label next to it so you can check your work.
How a compass is used in construction
Beyond simple circles, a compass is used to find a perpendicular bisector by drawing two intersecting arcs from each end of a line segment, to copy a length from one part of a drawing to another, and to construct regular polygons by stepping equal arcs around a circle. These constructions rely on keeping the same radius across multiple placements, which is exactly what the exact-radius field on this tool is for.
Using real units
By default, this compass works in arbitrary on-screen units, since a browser can't know your physical screen size without help. If you calibrate the online ruler on this site first, this tool automatically reuses that calibration so you can enter and read radii in real centimeters.
How do I draw a circle?
Click anywhere on the canvas to place the compass's center point, then drag outward from that point. As you drag, the two compass legs open to show the current radius. Release to draw the circle. Click elsewhere to move the compass to a new center.
Can I enter an exact radius instead of dragging?
Yes. Place a center point first, type a radius into the exact radius field, and select Draw at exact radius. This draws a precise circle at the current center without needing to drag exactly.
What units does the radius use?
By default, arbitrary on-screen units. If you calibrate the online ruler on this site first, this tool reuses that calibration to show real centimeters, millimeters, or inches.
Is this a magnetic or directional compass?
No. This is a geometry or drafting compass, the kind used to draw circles and arcs by hand. It has nothing to do with direction, headings, or magnetic north.
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