Impossible to say as everybody's mobile data usage requirements vary so much.
You should probably measure your data usage in Ireland for a few weeks to get an idea of what your usage is like and use that as a guide while bearing in mind that you may use even more abroad if you're using tourist apps, maps etc. more while on holiday.
Most smartphones these days have some sort of basic data usage monitor built into the Settings but there are also free and paid apps that give more functionality.
On the other hand if you're lying by the pool most of the time then they might have WiFi in which case your mobile data usage might be less than normal.
