Use the EPA's online radon map, which shows the predicted radon risk for any location in Ireland by grid square. The map tells you the likelihood that homes in the area exceed the reference level, but only a radon test in the individual house measures the actual level in that building.
The EPA publishes an interactive radon map covering the whole country. Entering an address or Eircode shows the predicted percentage of homes above the reference level in that grid square, which is the basis for deciding what radon protection a new building requires.
For an existing home, the map is only an indicator. A radon test uses small detectors placed in a living room and a bedroom for three months, which are then returned to a laboratory for analysis. Testing over a long period is necessary because radon levels fluctuate daily and seasonally.