I have been asked this a lot lately and it is something that I personally use myself. I try to not risk more than 1% of my total equity.
In AntSignals, to see what is your risk for each trade in % relative to portfolio value you can create a custom column. Here is how it looks:
We use two variables here: $risk and $portfolio. You need to add stop losses to your trade and portfolio initial value for this to work.