Scaling an Object Linearly
Scaling an object precisely is easy. If you want to scale all dimensions by a particular known factor, say half, select the object, and type 
to scale it and press 
. Type in the factor 0.5 into the Scale X field in the Resize panel, and press . Then select the 0.5 value in the Scale X box and drag it down to the other two boxes below. Click in the viewport to finish. This “dragging down” can sometimes be tricky to master, but persevere. If you just can’t get it right, then type 0.5 into the Scale Y field and the Scale Z field for the moment, and try again next time.
Scaling an object – Unevenly
It gets a little more complicated to scale the width, length and depth to different precise lengths.
We use the Measure mode 
together with 
to snap to the corners. Click here to read the article on Measuring.
Now let’s say we want:
- our length to be 4.5m instead of 4.32986m,
- our height to be 2.5m instead of 2.55694m and
- the depth to be 1.75m instead of 2m
We use simple proportion that we all learned at school, but we let Blender do the Math. We can scale in all three global axes. Let’s take a look at this object which is aligned orthogonally to all three axes:
To scale the object we click the Select Box mode 
, select the object, and type to scale it and press
Ignore the values in the Resize parameter panel, replace them with:
- 1/4.32986*4.5 for the X Scale (simple proportion)
- 1/2*1.75 for the Y Scale
- 1/2.55694*2.5 for the Z Scale:
We now return to Measure mode to check whether we didn’t have any “finger-trouble”:
Delete the old dimensions
Apply the scale 
Now re-dimension the object:
If you are scaling when the object sides are not aligned orthogonally with the Global axes, then you need to change the orientation in the resize parameters panel to Local:
The Bounding Box
Once you have an object ready to Scale to a specific size,it is useful to display the object’s bounding box. Select the object and click the Object Properties tab 
of the Properties Editor panel. Expand Viewport Display and click the checkbox Bounds :
A Bounding Box is defined as the smallest rectangular box the object can fit in. All internal angles are 90 degrees.
- The Bounding Box visually confirms what sides of the object are aligned with the global axes. Like a cross-check.
- It also gives us the ability to scale the object’s X, Y and Z components when it is not parallel to the axes, and that object must nevertheless fit into a specific volume.
What is a Bounding Box in Blender? – ScruffyFluffy 3D Learning
