In case you didn't know, Sketch is an awesome
vector, pixel, umm... "vecxel" design application for macOS. You can use it to design mockups, icons, screens and far more.
Some days ago I wrote a plugin for converting the pixels, that Sketch uses as a base unit to various real life units by using a DPI value and a factor. So when you export something in Sketch as a PDF, it will be exported with an DPI value of 72. Based on that you can very simply convert the pixel unit to every unit you want.
However, version 1.0 of the plugin wasn't quite well designed and the developer tools available at that time were very basic.
Also, version 1.0 used CocoaScript for the dialog UIs and that was a real pain.
Nowadays, skpm is available, a nice tool to build up the development environment for a Sketch unit. Additionally, one came up with a library that uses WKWebview for rendering sketch UIs in a browser window. This way I could simply wrap up a Bootstrap UI and some JQuery magic to build up my dialogs.