Roots of Reason
Roots of Reason
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squares inside, units around
Anchor Chart · Grade 3 · 3.MD.C.7 and 3.MD.D.8

Area and Perimeter

Area counts the squares that cover a shape. Perimeter counts the units around its edge.
1Area Covers the Inside
6 units4 units
6 × 4 = 24 square units
Count the squares or multiply the sides. Rows of equal squares make both answers agree.
2Perimeter Walks the Edge
6 units6 units4 units4 units
6 + 4 + 6 + 4 = 20 units
Walk all the way around and back to the start. Add every side once.
3Break It, Then Add
4 units2 units4 units4 × 44 × 2
16 + 8 = 24 square units
Split a hard rectangle into easy ones. The parts add back to the whole.
4Two Questions, One Shape
6 + 4 = 10
✗ sides added
that walk is perimeter
6 × 4 = 24
✓ squares counted
24 square units of cover
Area counts squares inside. Perimeter counts units around. The units tell you which.