Bitcoin – Transactions Per Second (TPS)

Transactions per second (TPS) is an important metric when comparing Blockchains and features in the Blockchain trilemma (security, scalability, decentralisation). Bitcoin is heavily criticised for its low throughput which is often suggested to be approximately 7 transactions per second. This would equate to approximately 4200 transactions of around 250 bytes in each block (based on a 10-minute block time). This size of the transaction appears optimistic given recent average transactions, meaning the actual performance is lower.

The Bitcoin network’s TPS is frequently compared to VISA, with a figure of 24000 oft-cited for their payment service. VISA themselves claim a capacity of 65,000 transaction messages per second (it is unclear if each transaction required more than one message). It is important to note that this is a suggested capacity of their network, not how many occur. Based on VISA financial reports, the average (mean) transaction throughput in recent years was between approximately 4500 (2020) and 6100 (2022).

But I digress…

The typical calculation for a Blockchain’s throughput is (block size/transaction size) / block time

In Bitcoin, in its current configuration (as based on target block time), this would be (1MB / transaction size) / 600.

The transaction size on the Bitcoin network is variable and therefore this isn’t a constant. Bitcoin Visuals (bitcoinvisuals.com) assesses the average Bitcoin transaction size in recent years (2017 to 2022) to be between 455 and 636 bytes. This would equate to a transactions throughput of between 2.75 and 3.84 transactions per second based on the target 10-minute block time.

As I’ve written previously, the 10-minute block time is a target and is most frequently beaten. This has an impact on the calculation of transactions per second. There are instances where blocks are found within a second of the previous block. If the mempool (where pending transactions wait to be included in a block) is full, or near capacity at this time then the spot transactions per second value could be very high.

I reviewed the block headers for all blocks up till block 772089 (15^th January 2023) and calculated the spot transactions per second for each block. In instances where a block was recorded as being mined earlier than its predecessor, the time difference was considered as a positive value.

Since the genesis block, Bitcoin has achieved approximately 5.7 transactions per second on average. The peak value I identified was 3087 transactions per second when block 572037 (16:02:17 17^th April 2019) contained 3087 transactions, and was mined within 1 second of block 572036 (16:02:17 17^th April 2019). It should be noted that this is one of the examples where the block height is positive, but the higher block is recorded as being mined earlier than the lower block emphasising the problems with the timing on the Bitcoin network.

The highest ‘non-negative’ time was in 2020 when block 649548 contained 3058 transactions and was mined one (1) second after block 649547 resulting in 3058 tps.

The table below summarises the last 12 years; in each of these years, there was at least one transaction a day.

If negative time values are ignored, rather than being inverted, the figures change slightly. These results are summarised below:

The increase in TPS from 2017 is expected, in part, the introduction of segwit to the Bitcoin protocol. By moving the witness data out of the block this allowed more transactions to be fitted within the 1MB block size.

Based on my previous experimentation with the accuracy of block timing where the average time between time in the block header and the time identified on my full node was 21 seconds then despite the findings above, they may not represent the throughput of the Bitcoin network. For example, if the timestamp of block 572037 was off by 21 seconds, then the TPS would go from 3087 to just 140. Still significantly higher than the expected throughput but lower than the summary figures would suggest.