Sixth Grade · Math · week 29

Surface area using nets

Use a net, the unfolded flat pattern, of a rectangular prism or triangular prism to find its total surface area.

A net is what a 3D shape looks like unfolded flat - every face laid out separately. Finding the area of every face in the net and adding them up gives the surface area of the whole solid.

A rectangular prism, or box shape, has 6 faces in 3 matching pairs: top and bottom, front and back, and the two sides. Find the area of one face in each pair, double it, then add all three doubled areas.

A triangular prism has 2 triangular faces (the ends) and 3 rectangular faces (the sides). Find each face's area separately and add them all together.

📋 For the teacher
Teach it (10–15 min):
  • Build or draw an actual net, cut it out, and fold it into a box so the "unfolding" idea is concrete.
  • Organize the six faces into their three matching pairs before adding, so no face gets counted twice or missed.
  • For a triangular prism, count carefully: 2 triangles plus 3 rectangles equals 5 faces total, not 6.
  • Double-check the total by re-tracing the net and confirming every face was counted exactly once.
Talk about it:
  • What is a net, and how does it help you find surface area?
  • Why does a rectangular prism have its faces in three matching pairs?
  • How many faces does a triangular prism have, and what shapes are they?

Mastery looks like: They correctly identify all faces in a net, whether a rectangular or triangular prism, and add their areas to find total surface area.

Common stumbles: Missing a face or counting one twice; using the wrong pair of dimensions for a face's area.

Homework for this lessonType it, write it with a stylus, or print it for pencil & paper.open →
Records attendance + 15 min of Math for this learner.
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