In Xcode 7.1 Simulator, when using ⌘+s
to save screenshot to desktop, it saves the actual size of the simulator. For example, iPhone 6 Plus 100%
sc
Uncheck "Optimize Rendering for Window Scale" option from "Debug" menu, if you want to save screenshot of actual device size
To take a screenshot of the iOS, watchOS, or tvOS device and save it to your Mac Clipboard
choose Edit > Copy Screen.
choose File > Save Screen Shot.
A screenshot of each open simulated device is saved to the desktop of your Mac.
@SamSol's answer may work for earlier versions of Xcode, but the debug window does not appear to be present in Xcode 11+.
Instead, I followed this suggestion from the Apple Developer forum:
The saved output image should have the desired resolution to be included on the Apple App Store.