Spin. Measure. Estimate.

SparkClass

Drag a ray around a real protractor, then connect degrees to a fraction of one full turn.

CCSS 4.MD.C.5a–b · 4.MD.C.6
Live Protractor
Drag The Coral Handle
Interactive semicircular protractor A baseline ray points right at zero degrees. A second ray opens counterclockwise to 45 degrees. Drag its endpoint or use the angle slider. 0° points right · 90° points up · 180° points left
01

Measure the opening, not the ray length. The second ray turns counterclockwise from the 0° baseline.

Angle45°
÷
Full Turn360°
=
Part Of A Turn1/8
Acute

From turning to measuring

Keep the focus on the opening between rays. The draggable endpoint changes direction, never the meaning of the angle.

1

Use landmarks before exact reading

Compare the moving ray with 0°, 90°, and 180°. Ask whether the angle is acute, right, obtuse, or straight before reading the scale.

2

Read the correct ray

The fixed ray starts at 0° on the right. Follow the moving ray to the outer scale. The major marks are 10° apart; each minor mark is 5°.

3

Connect degrees to one whole turn

Write angle/360, then simplify. At 45°, eight copies make one full turn, so the angle is 1/8 of a turn.

CCSS alignment: 4.MD.C.5a–b — understand angle measure and one-degree turns; 4.MD.C.6 — measure angles with a protractor. This lab measures angles from 0° through 180° in whole degrees.