Does doubling the number and adding 30 always work when converting something from metric to American?

Question

I read this somewhere and I know it works with temperature and distance. Does it always work?

Answer 1

It will get you close for temperature in the normal environmental range. It will give you nonsense applied to distance measurements.

Answer 2

i guess that depends on what you're converting. try doubling Km/h and adding 30, you'll get a speeding ticket. try doubling a meter and adding 30, you don't get a Yard. I think something in your theory is sketchy.

Answer 3

It should. Just look at Canadian canines. Canadian dogs are, in general, much younger than their American counter-parts because of the conversion. The (human years X 7) rule is exempt in this case.

Answer 4

I think it only works if you're north of the Equator. In the Southern Hemisphere, it's the opposite.