Why dont people all around the world use same units?

Basically Metric Rules its the best for any scientific application i am a canadian engineer and it pains me every time i have to use metric units because of American building materials and or companies have made metric units standard in construction. the conversions are so tedious and terrible inches, feet and pounds can all go to hell and die Americans are so stupid for not changing in the 60s like everyone else I hear that the cost of re-making all their roadsigns in kilometers would be in the billions thats one reason they will never change i ahte america

I've used my unit around the world.

By the whole world you pretty much have it. The only part is the united states and tradesmen in Canada.

Short answer - Momentum. THere have been many efforts to standardize on measurements - and I think many can tell you that the metric system "appears" to be gaining ground. But when you have populations that feel "ownership" over their "inches" and "yards" - well - the transition just takes so much time.

The US government initiated an effort to switch the US to the metric system in the early 70s, but it never got off the ground. Switching units is a really hard problem, and very expensive. It's not just a matter of how rulers and speedometers are labelled. The system of units that are in use affect, for example, the natural dimensions of things like screws and nuts. So, with the English system, the natural diameters for bolts might be 1/8, 1/4, 3/8, 1/2 of an inch. But in the metric system, the natural sizes are 4, 6, 8 10 millimeters. And these are not compatible. So, for a long time there would be a need to have BOTH sizes of bolts available, since there would be lots of "old" equipment around for many years. Some industries have gone to the metric system. I believe Boeing is now metric (starting with the 787). But when you start to think about how pervasive the measurement system is -- everything from yards in football to pints in a bar to .... you start to see that it's really a BIG job to change. Education, by the way, is an important part of it, since schools want to teach what's in use, but that tends to perpetuate the old ways.

You think that is bad, imagine what it was like when I was a boy at school, back home in Ireland: Imperial or Decimal ? – Confused as a Child. Twenty shillings made a pound, Twelve pence made a shilling. Twenty-four pence made a florin. Two shillings made a florin. Two sixpences made a shilling. Two shillings and sixpence made half-a-crown. Thirty pence made half-a-crown. Five shillings made a crown. FourCrowns made a pound. Two threepences made a sixpence. Ten threepences made half a crown. Eighty threepences made a pound. Forty sixpences made a pound. Two halfpennies made a penny. Two farthings made a halfpenny. Two hundred and forty pennies made a pound. Four hundred and eighty halfpennies made a pound. Nine hundred and sixty farthings made a pound. Twenty-hundredweight made a ton. Eight stone made a hundredweight. Fourteen pounds made a stone. Sixteen ounces made a pound, (Unless they were Troy ounces, then there were only twelve). Question: How many farthings were there in an ounce? ----------------------- Is it any wonder that I was forever getting a hiding from the teacher? (P.S. I have just noticed that there were in fact twenty pennyweights in a Troy ounce. Funny, but I learned this about fifty years too late) P.p.s. Not only did you have to learn them in English, but also in Gaelic................... (thinking about it makes me feel weak) --------------------