Dr Muhammad Hamza

the d-space equals the product of lattice parameter a (in case of cubic system) and the square root of the summation of squares of h, k, and l.

If your system is not cubic, then a further development to the above equation is necessary.

You can find useful information about your question from the previous question on ReserchGate at :

https://www.researchgate.net/post/How_to_calculate_lattice_constant_from_XRD_pattern .

Regards

Dear professer Ahmed Elsheikh the system is hexagonal.