What Will the Next Bitcoin Block Look Like?

Bitcoin transactions do not become part of the blockchain immediately after being sent. They initially enter the mempool, which is a continually changing collection of valid, unconfirmed transactions awaiting selection by miners. While a block explorer can display individual transactions and fee rates, it often does not provide a clear answer to key questions: How busy is the Bitcoin network right now?

How much data is waiting in the mempool? Which transactions may fit into the next block? Where is the current fee cutoff? Is the backlog growing or shrinking?

Bitcoin Mempool Monitor transforms this live queue into a compact visual overview designed for macOS users. Unlike a traditional block explorer, which may overwhelm users with raw data, this app presents a simplified visual representation of the mempool and block formation process.

Rather than providing a fixed countdown to the next block, Bitcoin Mempool Monitor shows a "Next Block Race" timer. This timer indicates how long the network has been waiting since the last confirmed block, but it does not predict when the next block will be mined. The app also displays the latest confirmed block and the number of transactions it contained, clearly showing the transition from the completed block to the current estimated block.

At the heart of the app's main view is a projection of which currently visible transactions could fit into one standard Bitcoin block if a miner were to select them at that moment. This estimated view provides several key metrics: the estimated transaction count, combined transaction fees, median fee rate, estimated block capacity, and the current fee cutoff point.

The capacity bar visually compares the selected transaction data with Bitcoin's block weight limit, indicating whether the block is close to being full. However, it's crucial to note that this is an estimate, not a confirmed block or a guaranteed miner selection.

Bitcoin Mempool Monitor offers a more nuanced view of transaction fees by presenting them as a distribution rather than a single recommendation. Transactions are grouped into fee ranges, such as "Below cutoff" (transactions outside the estimated block), "In range" (near the selection boundary), "Strong" (strong position for selection), and "Priority" (highest fee rates in the current view).

A vertical cutoff marker shows where the estimated next block ends, with transactions on either side of this line remaining in the mempool or fitting into the projected block. This dynamic visualization helps users understand how the fee market is changing over time.

To accommodate the significant difference in scale between the entire mempool and the estimated next block, Bitcoin Mempool Monitor employs two distinct visual scales. The left side of the app displays a compressed queue for transactions waiting beyond the next block, offering a broader perspective on the wider backlog. In contrast, the right side provides a more detailed map of the estimated next-block selection, showing the fee distribution among transactions that are competitive for the upcoming block.

While the app primarily focuses on the immediate next block, it also summarizes the broader visible mempool with key statistics: total waiting transactions, approximate block capacities, combined fees, and fast and economy fee recommendations. These contextual metrics help users grasp the magnitude of the backlog and its implications for the network.

Bitcoin Mempool Monitor is designed to be read-only, meaning it does not hold private keys, create transactions, or move funds. It functions as a non-intrusive observer of public Bitcoin network data, providing insights into the transaction queue, fee market dynamics, and an estimate of what may be included in the next block. The app offers contextual help through blue labels that open explanatory sidebars, demystifying complex blockchain terminology such as block weight, virtual bytes, fee rates, and mempool behavior.

By focusing on observation and education, Bitcoin Mempool Monitor serves as a valuable tool for Bitcoin users, developers, and anyone seeking to understand the intricate workings of the Bitcoin network between broadcasting a transaction and its eventual confirmation.