Maryland Math 3.GR.C.8
The Standard
Identify perimeter as an attribute of two-dimensional figures and measure the distance around the outside of a figure by counting units or adding lengths.
Maryland College and Career Ready Standards for Mathematics (2025) · UNDERSTAND CONCEPTS OF AREA AND PERIMETER.
Teacher's field guide
What This Standard Means
What Students Need to Do
- Students trace the outside edge of a flat shape and find its total length. They count unit edges on a grid or add the lengths of the sides.
What Mastery Looks Like
- A student counts each outside edge once, even when the shape has an indent. They add all side lengths and label the answer in units.
Common Misconceptions
- Students may count the squares inside the shape instead of the edges around it. They may count edges shared by two squares or miss a side when adding lengths.
How to Assess It
- Draw a 3-unit by 2-unit rectangle on a square grid. Ask students to trace its outside edge and write an addition sentence for its perimeter in units.
Lesson moves
Ways to Teach It
Give pairs square tiles and grid paper; have them build a shape, trace its outline, and count the exposed tile sides.
Show two shapes made from six tiles and ask, 'Do they have the same perimeter? How can you tell?'
Play Perimeter Match: students pair shapes on square grids with cards showing sums of their outside edge lengths.
Measure the four edges of a desk top with a tape measure, then add them to find how much edge trim it needs.
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Printable 3.GR.C.8 Worksheet
A ready-to-print activity worksheet aligned to 3.GR.C.8, with an answer key for the teacher on its own page. No account needed.
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Related Standards
- 3.GR.C.9
Solve problems in contexts involving perimeters of polygons, including finding the perimeter given the side lengths, finding an unknown side length, and finding...
- 3.GR.C.6
Identify area as an attribute of a two-dimensional figure and measure area of rectangular space by counting square units (non-standard equal-sized units, square...
- 5.GR.C.4
Identify volume as an attribute of three-dimensional figures and measure volume by counting cubic units (e.g., non-standard equal-sized units, cubic centimeters...
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