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The stipulated conventional cell is a square of side $2a$. Although introduced as a centered rectangular lattice, this equal-side case is a square Bravais lattice viewed with a rotated primitive basis. A corner-to-center separation iswhich is shorter than the $2a$ separation between adjacent conventional corners. Consequently the first contact of equal circles occurs atThe conventional square represents two lattice points: one from its four shared corners and one from its center. Its packing fraction is thereforeEquivalently, one circle occupies each primitive area $2a^2$. This is square circle packing; the drawing does not define a triangular close-packed lattice.

With the chosen basis, let ${\mathbf{b}}_1=(u,v)$. The reciprocal lattice conditions giveso $u=v=\pi /a$. Similarly, ${\mathbf{a}}_1\cdot {\mathbf{b}}_2=0$ and ${\mathbf{a}}_2\cdot {\mathbf{b}}_2=2\pi$ giveAll reciprocal points areThus, in coordinates measured in $\pi /a$, the two integer coordinates have the same parity. The reciprocal lattice is another rotated square Bravais lattice, with nearest-neighbor spacing $\sqrt{2}\pi /a$.