The US implements Imperial unit system instead of Metric. This has created lots of trouble for new comers. Among which, temperature and weight are the two of the most annoying ones.
Sure, we can slowly learn to adapt to the new system and do not convert unit in our head, but look, the problem is I have learned to use the Metric system all my life and as soon as I see the number, I am able to compare it to all of my past experiences so that I know what that number means. It’s just intuitive. In other situations where you need to compare the two when you don’t have a calculator at hand, what do you do?
Here’s my solution – Memorization:
For each degree of temperature changed in C, the corresponding change in F is 1.8 (~2). For each degree of temperature changed in F, the corresponding change in C is 0.56 (~0.5). With these value memorized and using the approx. values we do F to C conversion in our head.
For example, if today’s temperature is 76 F, that’s 8 degrees more than 68 F, which is 20 C, so 20 + 8*0.56 = 24.44. But how about using 8/2 instead? This way we can approx. 20 + 8/2 = 24, which is good enough.
For pound, it’s much easier. Each pound = half a kg x 0.9. Each kg = two pounds / 0.9.
I wrote this for the purpose of clarification.