--- title: "Measuring angles" description: "Measure angles in whole-number degrees using a protractor; draw given angles and sketch angles of specified measure" canonical: https://lightmysky.com/learn/mathematics/measuring-angles-mt_4MFUAsbx_6 source: https://lightmysky.com/learn/mathematics/measuring-angles-mt_4MFUAsbx_6.md retrieved: 2026-10-19 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Measuring angles Measure angles in whole-number degrees using a protractor; draw given angles and sketch angles of specified measure Subject: Mathematics · Area: Geometry · Ages 9 to 10 Page: https://lightmysky.com/learn/mathematics/measuring-angles-mt_4MFUAsbx_6 ## Ready when they can - Measure an angle with a protractor and read 47° - Draw an angle of 135° using a protractor - Identify which scale on the protractor to use for an obtuse angle ## Lesson: Measuring angles with a protractor Sometimes you need an angle's exact size. A standard semicircular protractor is a curved tool marked with two rows of numbers from 0 to 180. It measures a selected angle up to 180 degrees. The curved scale sits over the opening. Place its center point on the vertex. Align the printed baseline and zero with one ray. The printed baseline may sit above the physical bottom edge. Read where the other ray crosses, following the same row that starts at that zero. *(drawing: The recommended order is center on the vertex, one ray on 0, then read the mark.)* **Example.** Look at an angle where the protractor center is on the vertex, one ray lines up with 0, and the other ray crosses at the 47 mark. Follow the same row that starts at 0 on your aligned ray. Read 47. The angle measures 47 degrees. This is acute, a positive opening smaller than a right angle. A standard semicircular protractor has two rows of numbers, both running from 0 to 180. Each mark has two numbers, one on each row. At 90 both rows agree. Follow the row whose 0 sits on your aligned starting ray. Use the opening as a check: an acute angle, greater than 0 and under 90, reads under 90. An obtuse angle, greater than 90 and under 180, reads between 90 and 180. **Example.** To draw a 135 degree angle, first draw a straight ray. Place the protractor center on the ray's end. Align the printed baseline and 0 with the ray. Find 135 on the same row that starts at 0. Mark a point there. Draw the second ray from the vertex through that point. The two rows count in opposite directions from opposite baseline ends, so they add to 180 at every mark. To find the other row's number, subtract from 180. For example, 180 minus 152 is 28. Count up from 152 to 160 is 8, and 160 to 180 is 20, so 8 plus 20 is 28. **Recap.** Center on the vertex, align one ray with 0, then read the same row where the other ray crosses. Both rows run 0 to 180. Follow the row whose zero is on your aligned ray. ## Practice 34 questions on this page, each with its working shown. ## Needs first - [Geometric diagram conventions](https://lightmysky.com/learn/mathematics/geometric-diagram-conventions-mt_e4V6hvcuEJ) - [Types of angles](https://lightmysky.com/learn/mathematics/types-of-angles-mt_h0CVtqI2xo) - [Degrees and turns](https://lightmysky.com/learn/mathematics/degrees-and-turns-mt_qUGMyMYn9m) ## Opens up - [Drawing Ray Diagrams](https://lightmysky.com/learn/science/drawing-ray-diagrams-mt_-2VNlwAR5z) - [Angles that add up on a diagram](https://lightmysky.com/learn/mathematics/angles-that-add-up-on-a-diagram-mt_89riIKwGYp) - [Pie charts and line graphs](https://lightmysky.com/learn/mathematics/pie-charts-and-line-graphs-mt_bESTSBB0wK) - [2-D shapes (age 10+)](https://lightmysky.com/learn/mathematics/2-d-shapes-age-10-mt_hdrMoiTgqu) - [Choosing representations strategically](https://lightmysky.com/learn/mathematics/choosing-representations-strategically-mt_IwEOCN6bL1) - [Accurate drawing and scale diagrams](https://lightmysky.com/learn/mathematics/accurate-drawing-and-scale-diagrams-mt_Jf8xcX4UTq)