How to have a specific area in an irregular shape?

[Anonymous]

I modeled a form for my design project and now I have to scale it so floor areas have a specific amount (for example each floor should have 500 square meters area). I tried doing this with scale factor but because its original area has numbers after decimal I cant get that exact area that I need on each floor.

Am I doing something wrong? Is there another way?(Im using auto cad 2018)

[CADmonkey_UK_Building_Services]

On a real building site there is a tolerance of +/- 25mm. Maybe don't worry so much about getting 500.0000 square metres.

[Anonymous]

Thank you for your reply. I just wanted to know if there is a way to get the exact area if not I’ll do exactly as you said.

[CADmonkey_UK_Building_Services]

Maybe create a Block of your object? Then you can scale X and Y individually. This might help you find a way of calculating an exact scale factor.
Type DDUNITS to change how many decimal places are displayed (max=8).

[dbroad · Accepted solution]

Given the existing area, scale the object by the square root of the ratio of the desired area divided by the current area.

[Anonymous]

Thanks for replying 

I’ve actually done the things you’ve mentioned but they didn’t help 

[Anonymous]

Thanks for replying 

I’m not really good at understanding English mathematics. Do you mean:

(current area/desired area)² =scale factor

[David_W_Koch · Accepted solution]

@Anonymous 

I believe what he meant is this:

 

So, if the current area is 100 square meters, and the desired area is 150 square meters, the scale factor would be approximately 1.2247448713915890490986420373529.

[CADmonkey_UK_Building_Services]

Yup that'll do it

[Anonymous]

Yes because the scale factor is not accurate the desired area won’t be accurate ether . Is there no command or sth that I don’t know of in autocad that allows you to change the area of any shape to the desired number without using scale factor.

[CADmonkey_UK_Building_Services]

Now I'm confused. How is the scale factor "not accurate"? With DDUNITS you can display fractions of a millimetre to 8 decimal places.

David's formula works for me.

[Anonymous]

Looks like I’m not really good at explaining this In words. When I say its not accurate I mean the scale factor gives an area like 498.98 instead of the exact area of 500 because the scale factor might be a non-integer number

[Anonymous]

And when you remove the decimals it doesn’t mean that they’re really gone (I tried it and still got the same result)

[CADmonkey_UK_Building_Services]

David's formaula, applied to the numbers you mentioned, would look like this:

square root of (desired area / current area)
= square root of (500 / 498.98)
= square root of (1.0020441701070183173674295562948)
= 1.00102156325776435162615327964 (paste this into your command line as the scale factor)

[Anonymous]

I know how to use the formula and how to get a very long decimal for scale factor but I’m just trying to find deferent method sth that does not include scale factor calculation

[CADmonkey_UK_Building_Services]

Scaling seems like the best, if not the only, tool for the job. Can you provide more details?

[Anonymous]

Looks like there’s no other way other than scale factor in autocad for now. Thanks again for your reply

[dbroad]

@Anonymous  Sorry but I've been busy today.  This is what I did, starting from a polyline.

1. Select the object.
2. In the properties palette, select the calculator button next to area.
3. Copy the value (CTRL+C).
4. Start the scale command. Pick the object to scale. Select a basepoint and when it asks for the scale factor, enter
   'cal sqrt(<Desired area>/CTRL+V)

I marked my first response and David's as the correct answers. It is expected that the post/s that answer the question are accepted as solutions rather than the post that accepts the solution. I unmarked your response as a solution.

[Anonymous]

Thank you