2021 Oregon Math Guidance: 3.GM.D.8

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Cluster: 3.GM.D - Geometric measurement: recognize perimeter.


 Standards Statement (2021):

Solve problems involving authentic contexts for perimeters of polygons.


Preceding Pathway Content (2021)

Subsequent Pathway Content (2021)

Cross Domain Connections (2021)

Common Core (CCSS)






3.GM.D Crosswalk

 Standards Guidance:


  • Students should be given opportunities to develop a conceptual understanding of perimeter of all types of polygons including regular and irregular.
  • Students should investigate perimeters of polygons with a focus on quadrilaterals.
  • Students should be able to find the perimeter given the side lengths.
  • Students should be able to find the unknown side length given the perimeter.


  • The focus of this learning objective should be on developing the conceptual understanding of perimeter, rather than on terminology.
  • A polygon is a closed figure with at least three straight sides and angles; a polygon is regular only when all sides are equal and all angles are equal; and a polygon is irregular when all sides are not equal or all angles are not equal.

Teaching Strategies

  • Finding the perimeter given the side lengths;
  • Finding an unknown side length;
  • Showing rectangles with the same perimeter and different area;
  • Showing rectangles with the same area and different perimeters.
  • Students should solve contextual, mathematical problems involving perimeter and area of rectangles.


  • Perimeter problems for rectangles and parallelograms often give only the lengths of two adjacent sides or only show numbers for these sides in a drawing of the shape. The common error is to add just those two numbers. Having students first label the lengths of the other two sides as a reminder is helpful. Students then find unknown side lengths in more difficult “missing measurements” problems and other types of perimeter problems. (Please reference page 16 in the Progression document).


  • I have eighteen 1-foot panels to build a raised garden bed. How many different ways can I put these eighteen panels together to build a rectangular raised garden bed? Which rectangle will have the greatest area?