There is no global mempool, it's a per-node thing. I think the default for Bitcoin Core is to hold 300MB of transactions, which means for most nodes the number

There is no global mempool, it's a per-node thing. I think the default for Bitcoin Core is to hold 300MB of transactions, which means for most nodes the number of transactions in the mempool is constant. A better metric is transaction fees. Here's an example site: https://bitcoinfees.info/ https://bitcoinfees.info/