Mempool

The mempool (memory pool) is the holding area for transactions that have been broadcast to a network but not yet confirmed in a block. Each node keeps its own view of pending transactions.

How it works

When you send a transaction, it spreads across the network and waits in the mempool until a miner or validator selects it for the next block. Because block space is limited, those offering higher fees are generally picked first. Once a transaction is included in a confirmed block, it leaves the mempool.

Why it matters

The size of the mempool is a real-time measure of congestion: a crowded mempool means longer waits and higher fees, while an empty one means transactions confirm quickly and cheaply. Watching it helps users decide what fee to attach.

Example

During a surge in activity, thousands of transactions can pile up in the mempool, pushing fees higher.