The 2,500-Year-Old Trick That Still Works on Job Sites

Use the 3-4-5 Rule for Perfect Right Angles

(A Pro Tip for Amateur Remodelers)

Almost no carpenter could tell you who Pythagoras was—
But nearly all of them use his theorem on the job.

They just call it the 3-4-5 Rule.

This simple trick is how pros check whether a corner is truly square—and now you can use it to keep your DIY projects sharp and legit.

Here’s how it works:

• Measure 3 feet (or meters, or whatever) along one side of a corner.

• Measure 4 feet along the other side.

• Measure the diagonal between those two points.

• If the diagonal is exactly 5 feet, congratulations—that corner is a perfect 90 degrees.

📏 Why it matters:
Whether you’re framing a wall, laying out tile, or building a shed, bad angles lead to bad finishes. This little trick keeps your project square—literally.

And no, you don’t have to stick to 3-4-5. Double it to 6-8-10, scale it to 9-12-15…
The ratio is the magic.

Real estate investors who renovate properties should know this like they know ARV. A little math = a lot of saved headaches (and drywall).

Pythagoras would be proud.
Your contractor will be impressed.
And your walls? Perfectly square.