Mempool
The waiting room where broadcast transactions sit until a miner picks them up.
In plain words
A payment does not go "to Bitcoin" — it goes to every node's mempool: that node's own waiting room of valid payments hoping for block space. Miners fill blocks from theirs, highest fees first. When blocks are full, the line grows and the auction heats. When demand fades, it drains. There is no official mempool. Every node keeps its own, and they mostly agree.
Why it matters
- Watch it and you know the going rate before you send.
- Stuck payments explained: bid low, wait long.
- "In the mempool" is an opinion. In a block is a fact.
Numbers that matter
- 300 MB — Bitcoin Core's default mempool cap; lowest-fee payments drop first when it fills.
Go deeper
Updated 2026-07-29