Measurement: Perimeter, Area, and Capacity

Grade 3 measurement expands to four attributes with standard units: linear (cm, m, km), area (square units), capacity (mL, L), and mass (g, kg). Perimeter and area are introduced as concepts at this level: the focus is on understanding, not on formulas. The distinction between perimeter (length around) and area (space inside) is a conceptual landmark that students regularly confuse, and the confusion persists unless both concepts are developed together with concrete materials.