Why does my model measure like this?
The measurements are correct but the shape is just wrong for those sizes
It’s probably because you’ve re-sized it in object more. Blender still shows its original size. Try to apply the scale.
Thanks for the quick reply, but I don’t know what you mean by apply the scale?
Every time you scale something in object mode, blender keeps track of the change. You can “apply” it by Alt+R. The same goea for other transformations like rotating and moving.
OK, I’ll try that
I think Larson did a typo there, or this isnt sth i am aware of. But as far as i know alt R resets the current rotation of your object to its last known base state( the last you applied). To apply the scale you need to press Ctrl + A, this should open a menu where you see rotation, scale, location or apply all. This is what you need. Normally i just apply all, but this depends on the usecase ofc.
Yep, you’re right. I totally meant Ctrl+R. Using muscle memory I don’t even know what buttons I’m pressing most of the time 
You mean you totally meant Ctrl+A 
I think I’m gona take a break…