Quantifying achievements in CV

Dear members of WSO, 

It is strongly adviced to quantify one's achievments in CV (e.g. Achieved 180% year-over-year lead growth through strategic content marketing initiatives). While I certainly lead some projects and achieved something in my previous experience, I don't know how to quantify that (i.e. optimized processes by digitalizing, creating spreadsheets etc., but I don't know by how many percent it increased company's profitability or increased efficiency). Do people just make up those numbers or put up some approximate digits? 

I want to be honest and not include ungrounded information into CV.