Measure Angles Using a Protractor

Students use a protractor to measure angles in whole-number degrees. Students learn to align the protractor correctly (center at the vertex, baseline along a ray), choose the correct scale (inner vs. outer), and read the measurement accurately.

Try three of them

Real questions from this skill, graded here. No account, and nothing is saved.

Grade 4 · Measuring and Drawing Angles · question 1 of 3

0 of 20

20 rungs. A star at the top.

Record the opening of angle LOM in degrees.

Your answer:

How it is taught

0:00 of 3:54

A protractor measures an angle in degrees.

Center the hole on the vertex and line a ray up with 0.

Read it: Read from the ray on 0

Put the center on the vertex and one ray along the base line. That ray is on the inner scale's 0, so the inner numbers count the turn: the other ray is at 70, and the angle is 70°.

Put the center of the protractor on the vertex.
Line one ray up with the base line, on a 0.
Read from the 0 on that ray to the other ray: 70°.

Each scale counts the turn from its own 0, one from the right and one from the left.

The angle starts at the ray on 0, so only that scale counts this angle.

An angle narrower than a square corner is less than 90°, which checks the reading.

Read the numbers that start at 0 on one of the angle's rays. To make an angle, draw the ray at the mark.

Reading the other scale, and saying 110° for this angle.

110 counts from the other side's 0. The angle is narrower than a square corner, so it is 70°, less than 90°.

One ray is on 0 of the outer scale. The other ray crosses 135 on the outer scale and 45 on the inner scale. How many degrees is the angle? — 135. Read the outer scale, whose 0 is on the first ray: 135°.

Measuring a 70° angle

Here's an angle made by two rays meeting at a point. Let's find out how wide it opens — in degrees!

Grade 4 · Lining up the protractor and reading the right scale

A protractor is a half-circle ruler. It has a tiny crosshair in the middle and numbers from zero to one hundred eighty curving around the edge.

First, place the crosshair right on the vertex — the corner where the two rays meet.

Next, line up the flat edge along one of the rays. Keep it perfectly straight.

A protractor has two scales — an inner one and an outer one. Which one do we read?

Pick the scale that shows zero on our ray. Our ray points right, where the inner scale says zero — so we use the inner scale.

Now follow the other ray out to the curved edge of the protractor.

It points right at seventy on the inner scale.

Our angle measures seventy degrees! Nicely done.

Now you try. Read the protractor and type the measure. How many degrees?

What you see

While they climb, your page writes one true line to ask about tonight, and a short note each Sunday.

MayaGrade 3 · Mathematics

Did you know?

A chessboard has 64 squares — share them out between the 8 rows and each row holds exactly 8.

Today’s goal: 1 star — one skill mastered, every rung of its ladder climbed
Climbing now: Divide within 100

An example student.

MayaGrade 3 · Mathematics

Maya earned 2 stars this week — Interpret multiplication as equal groups, which took 6 answers over 3 days before its star landed 3 days ago and Multiply by 6, 7, 8 and 9. Next up: Divide within 100.

An example week.

More of the library

Every skill has a page

Practise this skill free

14 days of every skill, practice packets, Fluency sheets and up to four students. No card.

Start free