I finally got so many requests for a definition of the 3-4-5 rule that I quote so often in the lay-out part of many of my articles that I decided to post an article on it.

Other trades use it as well, but we carpenters depend on it like we do our 4 foot levels. The 3-4-5 rule is really just a practical extension of the Pythagorean theorem.

We use it when laying out post holes for a backyard deck (you know you want one), building a concrete form, or laying a finish floor.

What did Pythagoras have in mind when he published his mathematical proofs? Legend tells us that being a mathematician and philosopher, he considered this to be a huge deal. So much that he sacrificed some oxen to the Gods. I’m glad we don’t do that now!

Did you find this post helpful? Read more free DIY home improvement articles and bookmark us!

Anyhow, this is a basic thing for you to know before you build anything. The results are accurate, no expensive equipment is needed, and recall that all finish work rests solely on the shoulders of the prep work. So say I.