Free Interactive Triangle Calculator

Triangle Buddy is a free, visual triangle calculator that solves for missing sides, angles, and dimensions in real time. Drag any vertex to reshape the triangle and watch every side length and interior angle update instantly. Lock a side or angle to a fixed value, snap points to a grid or axis, and read results in both imperial (fractional inches down to 1/64") and metric (millimeters, centimeters, meters) units. No sign-up, no ads, works on desktop and mobile.

What you can calculate

  • Find a missing side of a triangle when you know other sides and angles.
  • Find a missing angle from known side lengths (law of cosines, solved automatically).
  • Solve right triangles, scalene, isosceles, and equilateral triangles.
  • Check whether three lengths can form a valid triangle (triangle inequality).
  • Convert triangle measurements between metric and imperial fractional-inch units.
  • Lay out a triangle to exact dimensions and read off every side and angle.

Who it's for

Students learning trigonometry and geometry, woodworkers and carpenters cutting angled joints, framers and roofers figuring rafter and rise/run angles, machinists and metalworkers, drafters and CAD users sketching layouts, quilters and crafters, tile setters, landscapers, and anyone who needs to solve a triangle quickly without installing software.

Frequently asked questions

How do I find a missing side of a triangle?

Drag the triangle's points until you know the values you have, then lock the known sides or angles by typing them in. Triangle Buddy solves the remaining side automatically and shows it in your chosen units.

Does it give measurements in inches and fractions?

Yes. Switch to imperial and every length is shown as a fraction of an inch, with selectable precision from 1/2 down to 1/64 of an inch, plus feet and yards. Metric mode shows millimeters, centimeters, or meters to up to four decimal places.

Is Triangle Buddy free?

Yes, it's completely free and there are no ads. It runs entirely in your browser.

Does it work on phones and tablets?

Yes. You can drag points with one finger, pinch to zoom, and pan with two fingers on touch devices, as well as use a mouse on desktop.

Triangle Buddy · a free interactive triangle calculator.