Measurement issue inside 9 inches walls by using Dimensions Tool

Could anybody assist me or advise me, I am new and in the learning process?

I drew a model of house 90’ X 50’ feet and then I draw boundary walls around 04 sides of 9" inches. My Dimensions tool is showing me outside measurement 90’ feet but in the side of the walls, the remaining space is 88’ 6" as well as another side outside measurement 50’ feet but inside of the walls the remaining space is 48’ 6".

As 1 foot is equal to 12 inches. IMeasurement issue inside 9 inches walls.skp (120.4 KB) am taking the each wall’s thickness is 9 inches so both side walls’ total width is 1 foot 8 inches.

If i will subtract 1’.8" of both walls’ space from 90’ then it should be 88’ 2"
Same like this, If I will subtract 1’.8" of both walls’ space from 50’ then it should be 48’ 6".

File is attached


**I think your math is incorrect. 88’ 2 " plus 1’ 8" would be 89’ 10" At least here in the US, 2 +8 = 10 not 12. SketchUp is showing the correct dimensions. And as Simon will point out, 9" +9" =

To confirm it for yourself, change the units to Inches and do the math.



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2 x 9" = 1’6" not 1’8" (or 20")

And I use metric!

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Thank you for your reply. you are saying right, I didn’t say Sketchup’s calculation is incorrect but I was confused between

2 x 9 = 1’6"

Again thank you for your time for your reply, sir, Not the matter of my mathematic, I was using a simple calculator, now using feet and inches calculator that solve my problem.



Methinks you need a new calculator!


Methinks we (USA) need a new measurement system.


You probably do but old habits die hard. We in the UK went metric (theoretically) in 1971. I was a teenager then and I am now nearing retirement. Ask anyone how tall they are, what they weigh (if you dare!), or how far to their nearest town, and most people will still answer in feet, stone, and miles respectively. Even people born after 1971! Buy a tape measure and it will almost certainly have dual imperial and metric readings.

About the only everyday thing that did change was our currency. We kept the words pence and pounds but shillings and pennies have pretty much disappeared.

I used to work with someone ten years older who hated going metric. His argument was that it is too easy to get a decimal point in the wrong place. So instead of being wrong by a factor of two (as in the above article) you might be wrong by factors of ten, a hundred, or a thousand (say). I don’t quite buy it as it is more obviously wrong if it’s that far out and so common sense usually kicks in. But for what I do, I am very thankful to Bonaparte.

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Same goes in Oz, with some things - even teenagers - and we went metric 40 years before they were born. I see it as just another example of how the “American way” pervades all forms of life here, through everything from movies to dual system tape measures. My daughter was even confused with the emergency phone number until her late teens. (ours is 000). A bit of topic and perhaps a tad political I guess - hope no one minds.