How this calculator works
For a cubic crystal, the plane normal has components proportional to h, k and l. Their squared sum sets interplanar spacing. Enter your measured lattice parameter rather than relying on a material name: composition and temperature can change it. A missing-index solve returns its magnitude; spacing cannot reveal its sign. Reflection intensities and systematic absences are outside this geometric calculation.
Formula
d_hkl = a/sqrt(h^2 + k^2 + l^2).
Worked example
For a = 0.4 nm, (100) gives d = 0.4 nm and (200) gives d = 0.2 nm. For (111), d = 0.4/sqrt(3) nm.
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Frequently asked questions
Can Miller indices be negative?
Yes. Their signs change orientation but not the cubic spacing given by this equation.
Does this work for hexagonal crystals?
No. Non-cubic lattices require their own metric and sometimes additional indices.
Can spacing uniquely determine all three indices?
No. Several families can share a spacing. A missing-index mode assumes the other two are known.