How this calculator works
Opposite faces form three equal-area pairs. The table shows which pair contributes most to the total. Removing the top subtracts one length-by-width face. Reverse area modes isolate one edge; the diagonal mode uses a spatial right triangle. These are geometric areas before seams, overlaps or cutting waste.
Formula
S = 2(lw + lh + wh); open-top area = lw + 2h(l + w); h = (S/2 - lw)/(l + w); d² = l² + w² + h².
Worked example
A 2 m by 3 m base and 4 m height give face pairs of 12, 16 and 24 m². The closed total is 52 m²; removing the 6 m² top leaves 46 m².
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Frequently asked questions
Which face is removed for an open box?
The top parallel to the length-by-width base. Rotate your measurements if a different face is open.
Can the area be too small?
Yes. For a positive height the total must exceed twice the base area.
Does the table include waste?
No. Its percentages describe the six ideal faces only.