--- title: "Estimating Angles" description: "Estimate and compare acute, obtuse, and reflex angles in degrees; classify angles by type and order them by size" canonical: https://lightmysky.com/learn/mathematics/estimating-angles-mt_YUJ5pwalqL source: https://lightmysky.com/learn/mathematics/estimating-angles-mt_YUJ5pwalqL.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`. # Estimating Angles Estimate and compare acute, obtuse, and reflex angles in degrees; classify angles by type and order them by size Subject: Mathematics · Area: Geometry · Ages 9 to 10 Page: https://lightmysky.com/learn/mathematics/estimating-angles-mt_YUJ5pwalqL ## Ready when they can - Estimate an angle as approximately 130° and classify it as obtuse - Identify a reflex angle in a diagram and estimate it as about 270° - Order four angles from smallest to largest by estimation before measuring ## Lesson: Estimating Angles You already know a full turn is 360 degrees and a quarter turn is 90 degrees. Estimating an angle means looking at it and guessing its size in degrees, before you check with a protractor. The best trick is to compare the angle to a right angle, which is exactly 90 degrees. *(drawing: At 3 o'clock, the clock hands form a right angle: exactly 90 degrees. Keep this picture in your mind as your measuring stick for guessing other angles.)* Angles have names based on their size. An acute angle is smaller than 90 degrees, like a narrow wedge. An obtuse angle is bigger than 90 degrees but smaller than 180 degrees, like a door opened wide. A reflex angle is bigger than 180 degrees, more than half of a full turn. **Example.** Priya looks at an angle that seems a bit wider than a right angle, maybe by a third again. She guesses about 130 degrees and calls it obtuse, since it's more than 90 degrees but less than 180. When she checks with a protractor, it reads 128 degrees. Her guess was close. **Tip.** To order angles from smallest to largest without measuring, sort by type first: acute angles come before obtuse angles, and reflex angles always come last, since they pass the halfway point of a full turn. **Recap.** Compare each angle to a right angle: acute is under 90 degrees, obtuse is between 90 and 180, and reflex is over 180. ## Practice 18 questions on this page, each with its working shown. ## Needs first - [Degrees and turns](https://lightmysky.com/learn/mathematics/degrees-and-turns-mt_qUGMyMYn9m) ## Opens up - [Regular and irregular polygons](https://lightmysky.com/learn/mathematics/regular-and-irregular-polygons-mt_8H2kO4k2B9)