At our bike shop based in Cork, Ireland we stock men's bike helmets, women's bike helmets and children's bike helmets in a range of sizes and colours.
We have the best selection of Cycling Helmets in Cork, possibly the country. We take head protection for cycling seriously. We have Road helmets which tend to be lighter and more vented, Mountain Bike helmets, Downhill MTB helmets, and commuting helmets in stock.
The main measurement that will be useful for you when ordering is your head circumference - you could find this by using a tape and measuring the distance around the crown of your head. See the image below, The first part explains this process. The second part may not be as useful -it gives Giro Helmet sizing onlly.