An eyeballed yard is roughly the same as an eyeballed meter. An eyeballed foot is 1/3 of that. You can stick 4 inches in 10 cm roughly.
And I just poke my nose out the window and look outside to see what the temperature is
Freezing.... ~30°F.... ~0°C
Need coat... ~50°F... ~10°C
T-shirt..... ~70°F... ~20°C
Melting..... ~90°F... ~30°C
Rules of thumb can be learned either direction!ps HN tables are not really a thing, are they?
pps Suspiciously many experiments are conducted at 293K
What you're ignoring is that a hundred plus or minus is a good range for average humans to grapple with and Fahrenheit splits the temperature swings in a given region across an approximately 100deg range.
So using Fahrenheit results in a pretty decent "as high as it can be without being clumsy" measurement system that covers just about all earthly temperatures.
If we only cared about increments of five or so degrees you could go higher resolution and it'd be fine because rounding would occur like we do with vehicle speeds. Or we could go lower resolution and just make the degrees bigger, which is basically what celsius is.