sure alot of signs in some countries would have to be changed but really Metric system is so much better. I am australian and we had the metric for an while now and i dont know how Americans and others manage with the imperial system. 

temperature seems crazy compare to celsius which is far easier than fahrenheit. 0 degrees celsius is freezing and 100 degrees is boiling, so if its below 0 degrees its going to snow or be really cold, if its around 30 to 40 its going to be hot. 

really easy and simple. I go look at fahrenheit and i go wtf was he thinking when he came up with 32 degrees for freezing and 212 degrees for boiling. 

But temperature isn't the only thing metric is vastly superior in, but also in mesurements. Again in metric: 10 mm = 1 cm, 100 cm = 1 metre, 1000 metres = 1 kilometre etc etc. An whats great is that weight and volume uses the exact same system.  And i wont go into miles and pounds, but my point has been put forward. 

Metric > imperial. 

So why dont everyone change to metric to universally have the same units of measurements and have an more clearer, easier more accessable form of measurement then the confusing unwanted slowly declining imperial system. 

Patriotism.

That's the only reasonable reason I can come up with what's keeping them from arriving at the 21st century.

Why not just mix them up like we do in the UK?

The annoying thing isn't the casual everyday use of imperial. That's fine, I don't really care.

It's when people use imperial in science and (especially relevant for me) engineering that it gets annoying. We have calculators now people! We love decimals!

how about everyone going ballistic?

I can think of a couple reasons:

1. People are stubborn and don't like change.  We've all grown up knowing what a mile is, an inch is, a pound is, etc.  Changing to metric would feel foreign and strange to many people.

2. People don't care about simplicity.  Really, they don't.  Again, people don't like change, so familiarity > simplicity in the eyes of most.

And if you think about it, the average person doesn't need metric.  If a person understands "inch" "pound" and "mile" but not so much "centimeter" "kilogram" or "kilometer" why should they have to change?  To satisfy some politician's dream to be "more modern" or "progressive" or whatever they come up with?

Scientists, should of course use metric.  It's basically the standard in science, and for good reason.  But for the everyday American use, who cares?  Not me.

Cause Americans then wouldn't know what a Quarter Pounder is anymore... Quarter Pounder >>> Metric system

That's a nice onehundredtwenty-five gram burger you have there.

The cost would be insane because nearly every road sign would have to be converted.

Not the ones that don't use Imperial, don't forget those