Two-line intersection
Two-Line Angle Finder
Measure the angle where two straight lines intersect — blueprint walls, UI edges, roof slopes or homework diagrams. Place the protractor center on the intersection (vertex), align each ray along a line, and read the angle live. Longer rays along the lines reduce placement error.
Updated Online Protractor
Keyboard: Tab handles, arrows nudge 1px center / 1° ray (Shift 10px / 5°), R reset, G grid, L lock baseline, Z undo, Shift+Z redo, +/- zoom. Endpoint magnifier shows while dragging. Drag center, baseline ray, second ray. Snap preview before commit. Image stays local — never uploaded. Press Esc to exit fullscreen.
Camera stays local — capture is processed in your browser
Tip: lengthen rays along the lines — short rays amplify vertex error. Use crosshair + magnifier + grid. Accuracy guide
Related angles — live
From your measured interior angle we calculate complement/supplement/reflex/radians (shown below the tool).
Two-line vs three-point
Two-line uses long edges; three-point uses a vertex + two points. Both are the same geometry — two-line guides you to lengthen rays for stability.
Keyboard precision — 1px / 10px
- Tab cycles center → A → B; focused handle shows outline.
- Arrows nudge 1px (fine). Shift + Arrows nudge 10px (coarse).
- While dragging a handle, axial nudge is 1° / Shift 5° snap — the magnifier shows endpoint detail.
- Beginner: keep snap 5°; advanced: set Off or 1° in More.
Mobile: handles are 44px hit targets; magnifier replaces hover precision.
Related
FAQ
What is two-line angle finding?
It measures the angle formed where two straight lines intersect. The vertex is the intersection; each ray follows one line. The tool shows the intersecting-line angle and its related complement/supplement/reflex.
Is it the same as three-point angle?
Three-point defines a vertex + two points; two-line defines two infinite lines. Both land on the same protractor center, but two-line emphasizes aligning along long edges for better ray length.