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 DIY Chatroom Home Improvement Forum My diagonal measurements say i'm square, but side to side disagree.
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04-15-2013, 09:57 AM   #1
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## My diagonal measurements say i'm square, but side to side disagree.

I had a concrete slab poured and am now laying one course of cinder block to get the walls off the ground.

I layed out blocks at the four corners and using the 3,4,5 formula figured out my diagonals need to measure 26' 11" which they do. However when I measure side to side I have one side that is 1/2" short and the opposite side is a 1/4" too long.

Of course if I adjust the block to correct those measurements it throws the diagonal measurements out of square. My question is, which measurement is the correct one? I'm assuming the diagonals. Or am I doing something incorrect?

04-15-2013, 10:03 AM   #2
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You know rectangles have right angles also. Is your slab a rectangle or square?

04-15-2013, 10:24 AM   #3
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Quote:
 Originally Posted by hammerlane You know rectangles have right angles also. Is your slab a rectangle or square?
rectangle 20x18

 04-15-2013, 10:33 AM #4 Member   Join Date: Sep 2012 Posts: 5,499 Rewards Points: 400 Accuracy isn't too much concern in the manufacturer of blocks so I suggest measuring outside to outside or inside to inside for both dimensions if you aren't.
 04-15-2013, 10:35 AM #5 Member   Join Date: Feb 2012 Location: Utica, NY Posts: 533 Rewards Points: 528 By the way, if you are off by 1/2" or less you are fine.
 04-15-2013, 10:35 AM #6 Maryland   Join Date: Jan 2011 Location: Eastern Shore, MD Posts: 413 Rewards Points: 250 Did you use 3,4,5 to confirm that your four corners are square? If all four corners are square and your footprint measures 18'x20', your diagonal measurement will be correct at just shy of 26'11".
04-15-2013, 11:17 AM   #7
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Quote:
 Originally Posted by Pittsville Did you use 3,4,5 to confirm that your four corners are square? If all four corners are square and your footprint measures 18'x20', your diagonal measurement will be correct at just shy of 26'11".
I haven't set any block yet, I just set one block on each corner and adjusted until my diagonals were the same. Then I planned to run string off those corner blocks as a guide.

So i'm good as long as my diagonals are measuring correctly?

 04-15-2013, 01:13 PM #8 Too Short? Cut it Again!   Join Date: Sep 2009 Posts: 9,634 Rewards Points: 2,000 Just a silly idea but why not use a framing square on this project? Last edited by user1007; 04-15-2013 at 01:17 PM.
 04-15-2013, 01:29 PM #9 Member     Join Date: Mar 2005 Location: Welland, Ontario Posts: 12,378 Rewards Points: 11,548 Blog Entries: 11 Measuring diagonals only makes a square IF THE OPPOSITE SIDES ARE THE SAME LENGTH. So make your sides the same length and then measure the diagonals for square.
 The Following User Says Thank You to joed For This Useful Post: concretemasonry (04-15-2013)
04-15-2013, 08:19 PM   #10
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Quote:
 Originally Posted by joed Measuring diagonals only makes a square IF THE OPPOSITE SIDES ARE THE SAME LENGTH. So make your sides the same length and then measure the diagonals for square.
Problem solved.

I should have said I used pythagorean theorem instead of 3, 4, 5

04-16-2013, 11:01 AM   #11
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Quote:
 Originally Posted by SubSailor Problem solved. I should have said I used pythagorean theorem instead of 3, 4, 5
In this case, same thing. A squared + B squared = C squared.
3 x 3 + 4 x 4 = 5 x5
I think thats where the 345 triangle came from.
Mike Hawkins

04-16-2013, 02:28 PM   #12
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Increasing to 6 - 8 - 10 ft. will give you a little more accuracy on a building the size of yours and on larger parcels 60 - 80 - 100 .

 The Following User Says Thank You to SeniorSitizen For This Useful Post: firehawkmph (04-16-2013)

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