How can you possibly have standardized measurement when there is no standard model for social ventures? Each venture can only measure what they do.
For example, we measure how many trees we plant per year (based on planting trees being inherent to our business model), how many dollars we're redirecting away from profit-focused businesses and toward businesses that are "for profit/for benefit" (again, inherent to our business), and how much we invest in organizations focused on solving climate change based on our 1% for the Planet membership. Aside from our 1% FTP membership, I'm not sure how you could possibly measure our impact against the impact of another, significantly different business.
As an aside, I can also tell you from working with hundreds of small businesses making a positive difference that most of them don't actively track their impact. They do things like support charity, have good labor practices, incorporate energy efficiency into their operations and sell low-footprint products/services because they personally believe it's the right thing to do. Most of them don't even advertise it. Conversely, large corporations like to drum up their CSR initiatives, track their impact and take every opportunity to highlight it but in my experience, they only do things that save them money and make them look good.