Mempool

The mempool, short for memory pool, is the waiting area where a Bitcoin node holds valid transactions that have been broadcast to the network but not yet included in a block. Every node maintains its own mempool rather than sharing a single global queue, and Bitcoin Core allocates 300 megabytes of memory to it by default.

Why it matters

The mempool is where Bitcoin's fee market operates. Miners select transactions from their mempools to fill the limited space available in each block, generally prioritizing the highest fee per virtual byte. When demand for block space exceeds supply, the backlog grows and users must bid higher fees to confirm quickly. During the inscription wave of May 2023, hundreds of thousands of transactions queued at once and fee rates briefly exceeded 300 satoshis per virtual byte.

Wallets read mempool conditions to estimate fees, and low-fee transactions can wait hours or days, or be dropped entirely when the pool fills.

In the gold vs bitcoin debate

Bitcoin's settlement queue is fully public, so anyone can audit congestion and pricing in real time. Gold settlement runs through vaults, courier schedules and dealer networks with no comparable public view. The mempool makes the cost of using scarce block space visible to every participant, a form of transparency that physical metal markets cannot replicate.