Every angle has a size you can measure in degrees, and a name based on that size. Once you can read a protractor confidently, you can measure anything from a doorframe to a slice of pizza.
An angle is formed when two rays share a common endpoint, called the vertex. Angles are measured in degrees (°) — a full circle is 360°, so a degree is 1/360th of a full turn.
This angle can be named ∠ABC or ∠CBA (the vertex letter always goes in the middle), or just ∠B if there's no other angle at that vertex to confuse it with.
When you see three-letter angle notation like ∠ABC, the middle letter — B — always tells you where the vertex is. The first and last letters just mark points along each ray.
Every angle falls into one of four categories based on its measure:
Less than 90°
Exactly 90°
Between 90° and 180°
Exactly 180°
To measure an angle: line up the protractor's center point exactly on the vertex, and rotate it until the 0° line lies right along one of the rays. Then read the number where the other ray crosses the scale.
Every protractor has two number scales — one counting up from the right (0° → 180°) and one counting up from the left (0° → 180°). Always start counting from 0° on the side where your baseline ray is. Reading the wrong scale is the single most common protractor mistake — a 40° angle can easily get misread as 140° if you grab the wrong number.
Try both activities: read a protractor to measure an angle, then use a virtual protractor to draw one yourself.
The angle is already lined up with 0° on the right. Read the inner scale.
Drag the orange handle to rotate the ray until it matches the target angle, then check your work.