What is Mempool?
The set of valid transactions a node has seen but that are not yet in a block — the queue competing for block space.
When broadcast demand exceeds the roughly four million weight units arriving every ten minutes, the mempool grows and the fee rate needed for prompt confirmation rises. When demand falls, it drains and fees fall.
There is no single global mempool. Every node keeps its own, with its own size limits and relay policies, so published mempool statistics describe one particular node's view.
A large mempool is congestion, not distress, and not a price signal. It reflects competition for block space and nothing else.
Related terms
Fee rate (sat/vB)
What a transaction pays per virtual byte of the space it occupies. Miners prioritise by fee rate, not by…
How it worksTransaction
A signed instruction consuming one or more UTXOs and creating new ones. Once confirmed it cannot be reversed.
Transactions & feesRBF (replace-by-fee)
A signalling mechanism that lets an unconfirmed transaction be replaced by a version paying a higher fee.
How it worksBlock
A batch of transactions accepted into the ledger together, produced roughly every ten minutes and limited to…
This definition is part of the Bitcoin Logical glossary. For the fuller explanation, start with Learn, or see the live numbers on The Bitcoin Signal.