Measuring Angles with a Protractor
Aligned to 4.MD.C.6 — Common Core State Standards for Mathematics.
What this lesson teaches
A protractor measures angles in degrees. Put its center point on the vertex and line up one ray with the zero line. Read where the other ray crosses the scale. Start from zero and count up to the correct number.
Worked example
Place the protractor center on the vertex and line up the bottom ray with 0. The top ray crosses the scale at 60. So the angle measures 60 degrees. To draw a 45 degree angle, mark a point at 45 on the scale and draw a ray from the vertex through it.
Practice questions
- An angle's ray crosses the protractor scale at 30. What is its measure?
- Explain in your own words where to place the protractor's center.
- Sketch an angle that measures about 90 degrees and label it.
Watch the lesson
Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.
▶ Watch this lessonEn español
Medir angulos con transportador
Un transportador mide angulos en grados. Coloca su punto central sobre el vertice y alinea un rayo con la linea del cero. Lee donde el otro rayo cruza la escala. Empieza desde cero y cuenta hasta el numero correcto.
Ejemplo: Coloca el centro del transportador sobre el vertice y alinea el rayo de abajo con el 0. El rayo de arriba cruza la escala en 60. Entonces el angulo mide 60 grados. Para dibujar un angulo de 45 grados, marca un punto en el 45 de la escala y traza un rayo desde el vertice pasando por el.
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