There are 2 ways to scaling a drawing in Autocad, Scaling by Factor and Scaling by Reference.
This tutorial will show you how to scale using Reference, you can read how to scale using Factor.
Scaling by a Reference
1 Make sure you have two objects to work with. This method is when you have a sized object, and you want to make another object to be the same length/size/proportion as the first one. For this method you need two objects to work with. One could be a line/object/block/image/group and the other could be different (eg. one line and one image, or one block and one image). Or they could both be the same thing (eg. two lines or two images).
2 Line up the two things so they have the same base point. Choose which object is the correct size for you, and leave it alone. Choose the thing you want to scale and click on it.
3 Type “sc” or “scale” and press ↵ Enter. Or choose the Scale button from the modify tab in the ribbon.
4 Specify a base point when asked. So select your base point (could be the point where the two objects line up).
5 Wait for the prompt bar to ask ‘specify scale factor or [Copy] [Reference]’. You can click on “reference” / or just type “r” and ↵ Enter.
6 Click on the base point of your object
7 Wait for the prompt to ask you to ‘specify second point’. You can select a midpoint of the object, or select the end, depending on how much you want to scale it. According to what you want, click on a point anywhere the object you want to scale. (Don’t click on the objects base point again.)
8 Specify a new length. Now you can click on how long you want the object to be. It could be to the midpoint of the first object, or it could be the full length of the first object. If you put the Object Snap (OSnap) off now, you can click anywhere in the workspace and your object will scale to that size.