Quite often you will have a monthly figure, when you want a weekly one, or a weekly one when you want a monthly one.
Monthly to weekly
Multiply the monthly figure by 12. This gives you the yearly figure. Then divide by 52.
Weekly to monthly
Multiply the weekly figure by 52. This gives you the yearly figure. Then divide by 12.
This is a straight mathematical exercise. It assumes that the figure you have is representative. If it is not, your result will be misleading. Say for example, that you use a week where the claimant was paid an unusually large or small amount, your monthly figure will be correspondingly large or small.