Lightning Network has been heavily promoted again recently as Bitcoin's most promising solution to scale globally and become the world's largest micropayments network. As Bitcoin's base layer (like most L1s) has high fees and longer waiting times, it's not suitable for small payments. Naturally, it makes sense to find out the limitations of the Lightning Network to understand if LN can indeed scale for billions of users worldwide. It's our understanding that the best source for finding out the capacity limits would be the LN Whitepaper itself. Fortunately, it has the answer.

If we presume that a decentralized payment network exists and one user will make 3 blockchain transactions per year on average, Bitcoin will be able to support over 35 million users with 1MB blocks in ideal circumstances (assuming 2000 transactions/MB, or 500 bytes/Tx).

This is quite limited, and an increase of the block size may be necessary to support everyone in the world using Bitcoin. A simple increase of the block size would be a hard fork, meaning all nodes will need to update their wallets if they wish to participate in the network with the larger blocks.

Block Size Increases and Consensus - Lightning Network Whitepaper

The section 10 of the LN whitepaper titled "Block Size Increases and Consensus" concludes that because of the current Bitcoin block size of 1 MB, Lightning Network can support just over 35 million users, assuming that each of them are performing 3 transactions per year on average. It's further stated that even this capacity is only possible under ideal circumstances (2000 tx / MB or 5000 bytes / tx), which is of course not always the case.

The latest version of Lightning Network whitepaper was released way back on 14 Jan, 2016 and little has changed on the Bitcoin base layer, since then. The Segregated Witness Consensus Layer (SegWit) was the most significant upgrade after the LN whitepaper release, resulting in the Bitcoin protocol being able to increase the number of transactions that it could process by removing the witness data, reducing tx size and raising the number of tx that can be included in the block.

It was introduced in Aug 2017 and according to the data obtained from Blockchain.com, the number of transactions that can be included in a single block now expand upto 2,500 tx / block under high load, against the 2,000 tx / block capacity, mentioned in the whitepaper. Assuming the same conditions, it means that the Lightning Network can now support just over 43.75 million users with the same 3 tx / year average.

The data shows that Lightning Network doesn't solve Bitcoin's scaling solution, the currently popular Strike and Chivo Wallets operate off-chain for the most parts and don't seem to use LN, in any true manner. Noting that the world's population is well over 7.8 billion and it's unlikely that each person can make only 3 transactions in a year, Bitcoin needs to increase its block size for the Lightning Network to work for everyone and fulfill its purpose in a truly decentralized manner.