The size and shape of the unit cell is defined by the lengths of the edges and the angles between the edges. The edges are named by the letters a, b, and c. The angles have the names alpha, beta, and gamma. These parameters are usually found from x-ray diffraction measurements.

The unit cells of metals are usually small. The unit cell of iron, for example, has dimensions a = b = c = 297 pm and alpha = beta = gamma = 90 degrees.

Remember, the edges of the unit cell extend between points with identical environments. Thus the edges of the unit cell connect identical points.