In cubic systems, interplanar spacing is defined as the distance between adjacent planes (hkl). According to Yong-ho Sohn, Ph.D., Assistant Professor of Advanced Materials Processing and Analysis Center at the University of Central Florida, interplanar spacing can assist in determining crystal structures. Matter.org states that the formula for interplanar spacing for a cubic structure is: d = a / (sqrt (h^2 + k^2 + l^2)), where "d" is interplanar spacing, "a" is the lattice parameter, and "h," "k" and "l" are plane indices.
Square the plane indices. For example, if your indices are 2,3 and 4, then 2^2=4, 3^2=9 and 4^2=16.
Add the squares of the plane indices together: 4+9+16=29.
Take the square root of Step 2: sqrt(29)=5.38516.
Divide the lattice parameter by Step 3. For example, if your lattice parameter is 4, then 4/5.58516=1.29987.