How do I resize the iOS simulator? I know that there's Window>Scale>100/75/50% but the scale of the retina iPad simulator is still too big for my screen to be able to test anything.

Is there a way I can scale the size of the iOS simulator smaller than one of the default values? I need it to scale down at least to 25% for my screen size to accommodate the window.
You can't. I've been an iOS software developer for two years and I haven't been able to find a way do this. I have tried to find solutions to this but came up with nothing. I'd love to be proven wrong, but I'm 99% certain there's no way to do this.

When my screen is too small I use 50% scale window, which is ought to be enough until I hook up my big monitor again at home.

EDIT: As of Xcode 9, you can resize it to any way you want from the corner of the simulator.