The buyers at The House of Bruar select the best quality and designs from UK and European suppliers, and consequently the sizes are not all standard. Please see the sizing converters below which show the conversion from European and US sizing to UK sizing.
 
UK/European Men’s Shirt Collar Sizing Converter:
UK Size (inches) 15 15.5 16 16.5 17 17.5 18
EU Size (cm) 40 41 42 43 44 45 46