If you are driving, from Westport take the coast road to Louisburgh (14 miles), drive straight through Louisburgh and about a quarter of a mile after passing through Louisburgh, (just after you pass by a small factory) take a right turn to Roonagh (the road is clearly signposted for Roonagh Pier and Clare Island.) It is a further 4 miles to the pier.
There are plenty of parking spaces near the pier.
The drive from Westport to Roonagh Pier takes about 35 minutes.