Definition. Stock-to-Flow (S/F) Ratio is a scarcity-based valuation model defined as the ratio of the current stock of a commodity (the circulating Bitcoin supply) to the flow of new production (newly mined bitcoins). The model assumes that scarcity drives value, and Bitcoin's price has historically followed the S/F Ratio, so it can be used to predict future Bitcoin valuations.

Notes. First coined by PlanB. For a detailed description, see Modeling Bitcoin's Value with Scarcity.