What is the mempool? Where crypto transactions wait to be confirmed
By SendPay Business · · 2 min read
The mempool, short for memory pool, is the waiting room for transactions that have been sent but not yet added to a block. Each node on the network keeps its own mempool, and miners pick transactions from it to build the next block.
How transactions leave the mempool
- You send a transaction and nodes pass it around the network.
- It sits in the mempool, marked as unconfirmed.
- Miners choose which transactions to include, usually the ones paying the highest fee for their size.
- Once included in a block, it has its first confirmation.
Why some payments wait longer
Bitcoin adds a new block roughly every 10 minutes and each block has limited space. When many people send at once, the mempool fills up, fees rise and low-fee transactions can wait hours or longer.
If a payment gets stuck
Some wallets let you raise the fee on a waiting transaction, known as replace-by-fee, or send a follow-on transaction that pays a higher fee to pull both through. Very old unconfirmed transactions may eventually drop out of most mempools.
Where SendPay fits
SendPay platforms let customers buy, sell and hold crypto, held with regulated partners, alongside GBP, EUR and USD accounts, powered by licensed partners. SendPay doesn't offer trading tools, DeFi or lending.
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This guide is general information, not legal or financial advice. SendPay Business is a technology company, not a bank, and does not take deposits; regulated services on the platforms are provided by licensed partners. PayPal, Patreon and Substack are named as reference points only and are not affiliated with SendPay Business.