- 4"x4" posts are actually only 3.5"x3.5"
Same type of thing on all measured boards, posts, etc..., due to cost-cutting policies that yield more lumber per tree by lying about measurements. Which is why that bookshelf project you tried ended up all oversized + freaky-looking + wouldn't fit together properly.
And why carpenters can overcharge and overcharge. They use some fuctup "new math"... and we're not talking about anything I got to study in school.
We covered Euclidean + non-Euclidean geometry, but 4=3.5?
That's some Orwellian geometry, there!