Every startup wants a sustainability slide, and almost every one measures the wrong thing. They report the office: the lights, the flights, the recycling bins. That is scope one and two, and for most software and product companies it is a rounding error. The real footprint is scope three: your supply chain, your cloud usage, the emissions baked into what you sell and buy. It is harder to measure, which is exactly why people avoid it. But reporting your tiny office footprint while ignoring the big one is not sustainability, it is decoration. Start with an honest estimate of the category that dominates your business, even a rough one. A real number about the thing that matters beats a precise number about the thing that does not.