This depends a lot on the kind of CSR initiative you are thinking of undertaking. If you invite your employees to participate in a beach clean up, then you can survey your employees about how the event makes them feel about the company, weigh the amount of trash that was collected and identify organizations that can help you translate that weighed trash into relatable terms like “saved 4 sea turtles from strangulation by plastic soda rings.”
In a less specific manner, you can benchmark against what other organizations are doing that are in your industry or are of a similar size, etc.