Bitcoin Mempool, Confirmations and Fee Rates
A Bitcoin mempool is a node’s local collection of transactions it considers eligible and not yet confirmed. There is no single globally identical waiting room or guaranteed queue position.
How it works
Nodes apply relay and resource policies in addition to consensus validity. Miners choose transactions under their own policies, often considering fee rate, dependencies and available block space. Fee rate is commonly satoshis per virtual byte. Confirmation counts indicate blocks since inclusion under the observed chain, not elapsed time guarantees.
Worked example
A transaction of 200 vB at 5 sat/vB offers 1,000 satoshis. Another of 100 vB at 8 sat/vB offers 800. The second pays fewer total satoshis but a higher rate per unit of space, which can make it more competitive. Ancestor packages and policy details can complicate a simple ranking.
Amounts, prices and scenarios are fictional teaching examples. They exclude any effects not explicitly stated and are not trade recommendations.
Limits and common mistakes
A wallet estimate can become outdated during congestion. Replacement or child-pays-for-parent options depend on transaction structure and node/miner policies; do not promise they always work. A screenshot showing “pending” does not establish that every node still holds the transaction.
Knowledge check
Must the transaction paying the largest total fee confirm first?
Read the explanation
No. Size, fee rate, dependencies, miner policies and the changing transaction set all affect selection.
References and further reading
- Bitcoin Developer Guide: transactions, blocks and consensus
- Bitcoin protocol improvement specifications
These sources explain the underlying concepts and specifications. They do not endorse QBMFX Academy. Check the relevant market, protocol version and reporting rules before applying an example.