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.
Perimeter vs. area
Perimeter is the total length around the outside of a shape: measured in length units (cm, m). Area is the amount of space inside: measured in square units (cm squared, m squared). A garden with a 12-metre perimeter could have many different areas depending on its shape. Two shapes with the same perimeter can have very different areas: a long thin rectangle has less area than a square with the same perimeter. This distinction must be established concretely before any formula is introduced.
Capacity and mass with standard units
1 litre = 1000 millilitres. A standard drinking glass holds about 250 mL. A litre of milk. A millilitre is very small (roughly 20 drops). For mass: a large paperclip is about 1 gram. A litre of water has a mass of about 1 kilogram (1000 grams). These personal referents connect the abstract units to physical experience, making estimation meaningful.
Circumference as a concept
The circumference is the distance around a circular object. The BC curriculum introduces this concept without pi or formulas: students measure circumference by wrapping a string around a circular object and measuring the string. Discovering that circumference is always about 3 times the diameter (roughly pi) is a profound mathematical discovery available through direct measurement.