This website provides a means to calculate various crystallographic parameters from unit cell parameters, such as the reciprocal cell dimensions and angles, matrices to convert fractional coordinates to orthogonal Cartesian form and *vice versa*, as well as the metric tensor and its inverse. In addition, the real and reciprocal unit cell volumes are calculated. It can also convert reciprocal cell parameters to real if they are input instead, but in that case note that anything refered to in the results as being for the 'reciprocal' cell will actually refer to the real one!

If Miller indices are entered in the box labelled "Plane *h, k, l* values", the *d*-spacing (or resolution) and the amplitude of each reciprocal lattice vector is calculated. If more than one set of indices is given, the angles between the plane normals (*i.e.* the interplanar angles) are calculated.

To determine the angles between real lattice directions, or zones, enter the *p, q, r* indices in the respective box and leave the box for *h, k, l* values empty.

If the user enters both Miller indices and zones or directions, the angles between the reciprocal lattice planes and the real lattice directions are calculated.

The formulae involved are described in more detail here. The matrices for converting between fractional and orthogonal coordinates use the PDB convention for aligning orthonormal axes with the unit cell vectors *i.e.* the *X*-axis is parallel with **a**, the vector **b** lies in the *XY* plane and *Z* is parallel with the reciprocal lattice vector **c***. This is described in more detail here.

Help is available in the tooltips which appear when you hover the mouse over text elements in the mid-bar.

This website was put together by **jbcooper_at_fastmail_dot_net** and use of it, or the code which can be obtained here, comes with no warrantees, etc. It is written in Lua and uses the lua-matrix library. Corrections and suggestions for improvement are gratefully received and please let me know if you find any bugs!