I think in inches; if you think in centimeters, here are conversions: 
    
    The inch is defined as 2.54 centimeters, therefore: 
    
1/8 inch = 0.3175 cm.  Call it a third of a centimeter. 
    
1/4 inch = 0.635 cm.  Call it a half or two thirds 
    
1/2 inch = 1.27 cm.  Call it a centimeter and a quarter. 
    
5/8 inch = 1.5875 cm.  Call it a centimeter and a half.         

1 inch = 2.54 cm.  Call it two and a half. 
    
4 inches = 10.16.  Call it ten centimeters.     

One foot is 12 inches.  Call it thirty centimeters.  (30.48) 

One yard is 36 inches.  Call it ninety centimeters.  (91.44) 
    
One meter is 40 inches.  (39.37 if you want to be picky.)