I am of the generation where we transitioned from imperial to metric. As such, I can't reliably think in either!
I like to buy my beer in pints, but my wine in centilitres. I buy diesel for the car in litres, but measure its consumption in miles per gallon (that's a British gallon, my Yank friends!). I have no idea how far 100km is, but if I've got to drive 100 miles I know exactly how long that will take me and how much fuel it will use. We're the only country in Europe still using miles on the roads, DON'T change it thanks very much!
I'm 6' 4" tall and 19 1/2 stone, no idea what that is in metres, or even pounds, but I know it's about 120kg. When Jay Leno says a car is 3500lb, I have no idea if that is heavy or light, but I can easily visualise 2 tonnes (not tons).
I weigh ingredients in grams if the quantity required is less than 200g, then I change to ounces and pounds for the larger quantities. Liquids (except beer) are litres and millilitres, I have no idea how big a fluid ounce is. I have absolutely no idea about Fahrenheit, temperature is always Celsius. When a yank says 'that's 150 degrees' I have no idea if that's hot or cold or what.
When I'm cutting timber to build something, I always measure it in inches and sixteenths, but when I'm fitting studwork the timber is always metric distances apart. Timber is always '3x2' or '4x4' and sheet wood is always '8x4' although I know that works out to be 2440mm x 1220mm. Steel RSJ and copper pipe are always metric, but pipe fittings are in inches BSP. Cable size is always metric: millimetres squared please, not SWG or AWG, or 'gauge'. Don't get me started on Newton-metres and pound-feet, or BTUs.
Nuts and bolts are ALWAYS metric, M6 thread with 10mm head I can understand, not 3/8 whitworth with a head that measures 18mm but you need a 32.6mm spanner or whatever it is. No idea about BA, or UNC or UNF or any of that. (I'm sure the
proper engineers like Robrenz on here will be:
).
I know how big an 0805 resistor is, but no idea what it is in metric; all my PCB designs have a metric board profile and metric fixing holes but an imperial grid. But critical component centres are placed on a metric grid, but tracks are routed on an imperial grid, with imperial widths and spacings, and imperial pad sizes, but metric drill holes, on 1 or 2 ounce copper.....
It's a fecking nightmare!