Notes
In order to be confirmed, a transaction from the mempool needs to be included in a block. Unlike the maximum size of a block which is fixed, the maximum number of transactions which can be included in a block varies, because not all transactions have the same size.
Methodology
Each Bitcoin node builds its own version of the mempool by connecting to the Bitcoin network. The mempool content is aggregated from a few instances of up to date Bitcoin nodes maintained by the Blockchain.com engineering team; this way, we gather as much information as possible to provide accurate mempool metrics.