Whether you are doing geometry homework, laying out wood joints for carpentry, or aligning architectural plans, measuring angles accurately is an essential skill. Follow this step-by-step tutorial to measure any angle quickly and precisely.
The 3 Core Steps to Measure Any Angle
1Align the Vertex
Find the vertex (the corner where two rays meet). Place the origin point — the small hole or crosshair at the center of your protractor's bottom edge — right over the vertex.
2Align the 0° Baseline
Keep the center point steady on the vertex and rotate the protractor so that the straight 0° bottom line rests directly on top of one of the angle's arms.
3Read the Degree Measurement
Follow the other arm out to where it intersects the curved scale. Count from 0° on your baseline arm to read the angle accurately.
Measuring Different Types of Angles
Acute Angles (0° < θ < 90°)
Sharper than a square corner. Always double-check that your reading is less than 90°.
Right Angles (θ = 90°)
Forms a perfect perpendicular corner. Both inner and outer scales point to 90°.
Obtuse Angles (90° < θ < 180°)
Wider than a square corner. The reading must always be between 90° and 180°.
Reflex Angles (180° < θ < 360°)
Greater than a straight line. Measure the inside angle and subtract from 360°, or switch to our 360° full circle protractor.
Measure Angles on Photos or Worksheets
No physical protractor handy? Upload any photo to freeProtractor and measure with 0.01° sub-pixel precision.
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