4th Grade Geometry · CCSS 4.MD.5 & 4.MD.6
Angle Explorer & Interactive Protractor
Make and measure angles from 0° to 180°. Use the protractor to find the number of degrees.
∠ABC Make an Angle
Try it: Drag the blue dot Point A or use the buttons on the right.
Reading: Inside 0° Scale
45
°
📐
Acute Angle
Greater than 0° & less than 90°
Acute Angle: Sharp and narrow! It is smaller than a standard square corner (90°). Think of an open scissors or a slice of pizza!
💡
How to Read the Protractor
The protractor has two rows of numbers. Start at the row with 0° next to the black line.
Inside Scale (0° on Right)
45° ✓
Outside Scale (180° on Right)
135°
Helpful Angles
Click one
🎯 Mystery Angle: Use the protractor to measure the angle. How many degrees is it?
Bullseye! 🎯
You got the exact measurement!
Acute Angle
< 90°
Smaller than a right angle. Sharp like a slice of pie or bird's beak. Common examples: 30°, 45°, 60°.
Right Angle
= 90°
Forms an exact square corner. Marked with a small square symbol. The foundation of perpendicular lines!
Obtuse Angle
90° – 180°
Wider than a right angle, but less than a straight line. Like an open laptop screen or reclining beach chair.
Straight Angle
= 180°
Forms an exact flat line. Equal to two right angles together (90° + 90° = 180°) or half a complete circle.