345 rule, trade secret, everybody should know this trick

This is one of the handy tricks used by builders and makers, taking advantage of the convenient hypotenuse of 3 x 4 dimensions

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[shealdedmon]

Everybody that needs to know it already does. It's one of the first things a flooring installer learns.

[tspis]

And yes, this is basic high school geometry - but no need for anyone to feel bad. Some people just forgot, others fell behind in school and got convinced they “suck at math”, so never caught up, and some have genuine learning disabilities.
We all have things we’re better at than others, and things that challenge us that other people find easy. Fortunately, we got YouTube and the like to help us all learn, teach, and share.

[That.Guy.]

Trade secret?!?! Pythagoras has entered the conversation…

[nickyleblanc]

As a grounds keeper in a school district for 20 years, this was very handy in setting up all our sports fields.

[toddwilliams]

Ya, one of the first things I learned when I began framing, but you got it wrong, bud the diagonal is the 5' foot span, lol the 90* spans are 3' and 4' the diagonal to ensure it is square is a 5' length

[markbrajkovich]

Thank God he made this video. I couldn’t find only but two or 300 of the same video.

[BobBob-ehsb]

A squared plus B squared = C squared. 3 squared is 9. 4 squared is 16. 5 squared =25. 9+16=25. Also works with 6, 8, and 10 and so on. As said in another comment, it’s the Pythagorean Theorem.

[AlexandruVoda]

The thumbnail with the hypotenuse being 4 is very triggering.

[psidvicious]

Giving the actual formula on why this works would have been helpful. It’s called The Pythagorean Theorem.
A²+B²=C² - ‘C’ is always the diagonal (hypotenuse)
You can use any numbers you want for ‘A’ and ‘B’. 3-4-5 is nice because it works out to whole, easy to remember numbers, without any decimals or fractions. 
Example - If ‘A’=3 and ‘B’=4 then ‘C’ will = 5 —— 3²+4²=5² or 9+16=25

If ‘A’=10 and ‘B’=19 than ‘C’ will = 21.4709 —— 10²+19²=21.4709² or 100+361=461 (√ 461= 21.4709)
Obviously not as clean looking but works and proves the theorem.
Btw, √ is the sign for square root. Which is the opposite of ( ² ) squared. 10² =100 or √100 = 10

Everyone has a phone with a calculator that has a square root ( √ ) function on it, so no one should be afraid to tackle uneven numbers anymore. Your phone will do the hard work for you. You just need to know what to tell it to do 📱

[dosgatosnegros]

I was going to guff this, then I decided to actually pay attention.

This really is powerfully valuable!

[marksmith]

I don't know if you know but the 345 rule is become obsolete, it has been replaced I think 8 years ago by the 6810 Factor.

[malakai]

I learned this years ago and have been using it ever since. Another tool that helps is to measure corner to corner diagonally both measurements should be the same.

[dantheman]

I've known this since I was a kid. Still use it today

[steveglover]

Pythagorean Theorem : for any right triangle, the square root of the sum of squares of the two shorter sides equals the length of the third side. 3, 4 and 5 are the shortest lengths that make for easy answers when calculating squares and square roots. Given the lengths of any two sides the length of the third side can be calculated by an algebraic rearrangement of the formula, A(squared) + B(squared) = C(squared)

[hewittzhotwheelz]

You can also multiply any distance in A times itself, then multiply any distance in B times itself, then add the 2 numbers together and square root the total to end up with the distance for C 😊
36x36=1296 48×48=2304 - 2304+1296=3600 - sq root(3600)=60 works with any distance. Sorry, my keyboard wont show me the Sq Root symbol for some reason.

[mfrank]

I did flooring and our school is teaching apprentices to swing arcs to square a 90 degree line from the main lay line. Tape measures bend and we don’t have thirty foot long straight edges. It’s dumb and disastrous if you’re in a large room and staring out of the center. They also don’t understand what a high line is for either.

[sonsofliberty]

For anyone who cares. A²+B²=C² so take your measurements on 2 sides A²+B². Then, take the sq root of that total to get your diaganol line.

[marck]

learn this in the first week as carpenter apprentice, I tend to use a laser cross line these days:) much faster!

[powerwagon]

Or use- (X squared plus T squared) squared root. Or (3x3 + 4x4)=25 square root is 5. Works for all numbers. Or buy a builder’s calculator and use run, rise and diagonal feature.

[dantheman]

Alot of people don't know what a water level is either. That comes in very handy if used right