I can use grids for desktop measurements. But, for mobile, I can't figure out how to show the measurements (padding, alignment) for developers.
I've found a lot of insights looking into how Google is presenting Material Design. It's speaking a common designer/developer language. It's worth studying it and implementing concepts from it to your specifications.
As for measurements, just stay out of pixels and everything should be ok. It can get really confusing, but with a bit of patience everything will make sense at some point. This article explains it really well (grab a cup of coffee/tea before starting it): http://sebastien-gabriel.com/designers-guide-to-dpi/
You can use Sketch and Zeplin, like @ILikeBeansTacos said. In addition to that, every element I design has a variable name the developer and I thought of so when he sees the designs in Zeplin he knows what elements I'm using.
I also create an artboard where I put all my elements so the developers have a 'style guide' artboard in Zeplin.