Quick way to make a rectangle of exact dimensions

I want to 3D-print a name sign. I need to make a rectangle that’s 28mm by 5.5mm.

I know a few clunky ways to do this by eye, but what’s the most efficient way? My goal is to be sure that a given shape is exactly the measurements I need.

Entering the numbers in the N panel doesn’t help because, when I change the X size, the other dimensions change, too. Clicking the locks by the “Scale” fields doesn’t affect this; it behaves the same.

I’m missing some “duh!” obvious thing here, right?

See image.

Create an image in Gimp or Photoshop that is there exact size you need then import it into Blender using the Image To Plane AddOn.

Rich, that’s helpful to see. What your image shows is exactly how I tried to resize the object. I made some new cubes and planes, and they’ll resize properly. I can change the X dimension without affecting the Y or Z. These 2 clues suggest to me that I’m doing it right.

I don’t know why it was happening, but some of my objects wouldn’t let me change a single dimension without it changing the others. When I change the X dimension, for example, the other dimensions change, too. The object maintained its proportions.

I couldn’t find a way to make that stop. If there’s a toggle or setting that forces an object to maintain its proportions of width, height & depth, I couldn’t find it.

Thanks, Rich and Atom.

You have Delta Transforms Scales different than 1.

Oooh, now I see that. Of course you’re right.

I don’t know how the “delta transform” fields get their numbers. I don’t know why they’re different, because I didn’t intend to change them.

Thanks for this hint. Now I know where to look if this happens to me again.