Market Cap is the spot valuation of issued BTC supply: circulating supply marked at the current USD price. In mature periods the series is dominated by price, while issuance adds only a slow mechanical drift. It is the fast side of the market-versus-realized valuation pair.
A rising Market Cap usually reflects repricing faster than supply growth, while a decline is almost entirely a price event. The level is most useful against Realized Cap, MVRV, or NUPL, where the question is not size alone but how far spot valuation has detached from aggregate cost basis.
The metric applies the marginal market price to the full circulating supply. That is standard, but it overstates what could actually clear at that level and leaves lost coins inside the denominator. For cost-basis work or capital stored on-chain, Realized Cap is the cleaner reference.
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