The short answer: the mempool ("memory pool") is every bitcoin node's holding area for valid transactions that haven't yet been included in a block. When you send bitcoin, your transaction doesn't go to anyone — it goes to the mempool, propagating node to node, where it waits for a miner to pick it. Right now there are 82,340 transactions waiting (live number). Miners choose by fee rate, which makes the mempool something much more interesting than a queue: it's a continuous auction for block space.
The journey of one transaction
- Broadcast. Your wallet signs the transaction and hands it to a few nodes.
- Validation. Each node checks everything — signatures, no double-spend, rules — before accepting it. Invalid transactions die here, instantly, for free.
- Relay. Valid transactions ripple across the network in seconds. Within moments, thousands of independent mempools contain your transaction.
- Selection. Miners assemble candidate blocks, packing the highest fee-per-byte transactions first — pure economics, no favorites.
- Confirmation. A miner finds a block; your transaction is sealed into the chain and leaves every mempool at once. It now exists forever.
There is no "the" mempool
The singular is a convenient lie. Every node maintains its own mempool — its private opinion about what's waiting. They agree heavily (relay sees to that) but never perfectly: nodes cap mempool memory and purge the cheapest transactions when full, apply slightly different policies, and hear about transactions at different moments. When you see "the mempool" on a dashboard — including ours — you're seeing one well-connected node's view. For reading conditions, that's plenty; just know the map is not the territory.
How to read it before you send
The mempool is the only honest fee oracle. Deep and rising → the auction is hot, either pay the priority rate or wait. Shallow → the economy rate confirms fast and it's the moment for cheap housekeeping (consolidations, batch payments). Traders read it too: a flood of transactions into the mempool during volatility is the network's pulse quickening in real time — often visible minutes before anything shows up in a headline. It's the same signal our Wallet Watch exploits: the chain always knows first.
Questions people actually ask
Is there one global mempool?
No — that is the most common misconception. Every node keeps its own mempool, its private view of the waiting room. They converge because nodes relay transactions to each other, but they are never identical: policies, timing, and memory limits differ node by node.
How long can a transaction stay in the mempool?
Until it confirms, is replaced, or gets evicted. Most nodes drop transactions after about two weeks, and when the mempool overflows its memory limit, the lowest fee rates are purged first. Evicted coins never leave your wallet — the transaction simply stops existing.
Why did my transaction disappear from the mempool?
It was either confirmed into a block, replaced via RBF by a higher-fee version, or evicted by purge rules. If evicted, your wallet can simply rebroadcast or re-send with a higher fee — the funds never moved.
What does it mean when the mempool is “empty”?
That the next block can fit essentially everything waiting — so the fee auction has no pressure and minimum-fee transactions confirm quickly. An empty mempool is the green light for cheap consolidations and low-priority sends.