Overview
Stock-to-flow (S2F) is a ratio that measures the scarcity of a commodity by dividing its existing stockpile (stock) by its annual rate of production (flow). A high stock-to-flow ratio indicates that the commodity is scarce relative to its new supply — it would take many years of production to double the existing supply. This concept has been applied to precious metals for decades and was brought into the Bitcoin discourse as a framework for understanding Bitcoin's programmatic scarcity.
Gold has historically had the highest stock-to-flow ratio of any commodity, at roughly 60-65 (meaning it would take over 60 years of mining at current rates to double the above-ground supply). Bitcoin's stock-to-flow ratio doubles with each halving, and after the 2024 halving it surpassed gold's ratio, making Bitcoin the "hardest" monetary asset in existence by this measure.
How It Is Calculated
Stock-to-Flow Ratio = Existing Supply / Annual Production
Example (post-2024 halving):
Stock: ~19,700,000 BTC in circulation
Flow: ~164,250 BTC mined per year (3.125 BTC × ~52,560 blocks)
S2F: ~120
For comparison:
Gold S2F: ~62 (200,000 tonnes above ground / ~3,200 tonnes mined per year)
Silver S2F: ~22
Platinum: ~1
Fiat: ~0 (effectively unlimited new production)
The S2F Price Model
In 2019, an anonymous analyst known as PlanB published a model that used Bitcoin's stock-to-flow ratio to predict its market value. The model plotted a logarithmic regression between Bitcoin's S2F ratio and its market capitalization across halving epochs, producing a strikingly linear relationship on a log-log scale. The model suggested that Bitcoin's price is fundamentally driven by its increasing scarcity, and it successfully described Bitcoin's price behavior across its first three halving cycles.
The model gained enormous popularity in the Bitcoin community because it provided a quantitative framework that aligned with the intuitive belief that Bitcoin's fixed supply makes it inherently valuable. It also made bold price predictions that, for certain periods, tracked remarkably closely with actual market prices.
Criticisms and Limitations
The stock-to-flow model has faced significant criticism from both mainstream economists and within the Bitcoin community itself:
- Demand is ignored: The model is purely supply-side. It assumes that demand grows proportionally with scarcity, which is not guaranteed.
- Sample size: With only four halving epochs of data (and only three completed when the model was published), the regression has very few data points, making it statistically fragile.
- Cointegration issues: Critics argue the apparent relationship may be spurious — two rising time series (S2F ratio and price) will appear correlated even without a causal link.
- Falsifiability: Some argue the model's wide confidence intervals make it difficult to falsify, as nearly any price outcome can be framed as "within range."
Despite these criticisms, the stock-to-flow framework remains valuable as a mental model for understanding Bitcoin's monetary properties, even if it should not be treated as a precise price prediction tool.
Related Concepts
- Halving — the event that doubles Bitcoin's stock-to-flow ratio every four years
- Inflation — stock-to-flow is the inverse way of expressing Bitcoin's declining inflation rate
- Mining — the process that produces the "flow" in the ratio
- Sound Money — the monetary philosophy that values high stock-to-flow assets