For calculation of your hourly rate we consider we consider a quarter (3 months time) because not every month has exactly 4 weeks. Within three months time there is 13 weeks.
Let’s say then that your gross salary is €2100 per month:
We take into consideration three times your monthly salary which is: 3x2100= 6300. Within those three months time you should work 520 hours (13 weeks x 40 hour per week). When calculating hourly rate we simply divide 6300 by 520 and we get €12.12 per hour gross.
Even though on weekly bases it can seems to be lower, on a monthly bases it is exactly what you should receive.