🧱 See It
Recall the net idea: surface area is simply the total area of every face in the net, added together. For a rectangular prism (a box), the six faces come in three matching pairs: top/bottom, front/back, and left/right.
✏️ Draw It
A real 3D box, with its three different face dimensions labeled:
Three DIFFERENT face shapes here — front (length × height), top (length × width), and side (width × height) — each one appears twice in the finished box.
🔢 Write It
Surface Area = 2(length × width) + 2(length × height) + 2(width × height)
Find the area of one of each of the three different face shapes, then double each one (for its matching partner on the opposite side), then add all three doubled amounts together.
Three different face shapes, each doubled, then all added together. Never just one calculation — three separate pairs.
💡 Worked Examples
Example — A box measuring 4 cm × 3 cm × 5 cm:
- Top/bottom pair:
4 × 3 = 12, doubled =24 - Front/back pair:
4 × 5 = 20, doubled =40 - Left/right pair:
3 × 5 = 15, doubled =30 - Add all three:
24 + 40 + 30 = 94 - Answer: Surface Area = 94 cm²
🧠 Quick Reference
Three pairs of matching faces. Find the area of ONE face from each pair, double each one, then add all three doubled amounts together. Never forget a pair — six faces, three pairs, no exceptions for a rectangular prism.