In blockchain technology, a transaction is never instant. It can only take place once a block containing the transaction data has been generated. The time needed to create this new block is called block time.
What is block time?

Block times are not the same for every cryptocurrency. Some protocols support faster block times than others. Depending on the blockchain network, a new block is mined in a matter of seconds or it can take a few minutes to be generated.

Many major blockchain networks, like Bitcoin, Litecoin, and Bitcoin Cash, are based on the proof of work mining algorithm. These protocols change their mining difficulty every time a set number of blocks is mined. The difficulty is increased or decreased so that the average block time remains the same.

BLOCK TIME ESSENTIALS

  • Block time is the average time needed to mine a new block.
  • Blockchain networks have different block times.
  • Block times range from a matter of seconds to a few minutes.
  • With proof-of-work-based blockchains, the block time is maintained close to a constant value by re-evaluating the mining difficulty.

Block times of major blockchains

There are two types of block times that you should be familiar with. The one you will come across most often is expected block time. As the name suggests, it is the expected time required to generate a new block. This number is pre-determined for every blockchain.

Blockchain

Exp. block time

Bitcoin

10 min

Ethereum

10–19 s

Litecoin

2.5 min

Bitcoin Cash

10 min

The expected block times of major blockchain protocols.

The other block time value worth mentioning is average block time. This is how long it actually takes the miners to mine a new block, on average. Block times can change a lot from block to block, because mining is based on a variety of factors, including luck. That is why we look at average block times instead of individual block times.

Average block time and expected block time are used to calculate mining difficulty.

Mining difficulty

Mining difficulty measures how hard it is to find the hash for a given difficulty target. The higher the target is set, the longer a miner requires to discover the hash for a given target. The mining difficulty target is re-calculated automatically based on how much computing power is available in the network in total. This is done to enable new blocks to be mined at a constant rate.

If the average block time is faster than the expected block time – usually due to new miners joining and more computing power becoming available in the network –, the difficulty is increased, so that the average block time becomes slower. It also works the other way around if the total computing power in the network is diminished.

In the case of Bitcoin, the level of difficulty is re-evaluated every 2016 blocks or approximately every two weeks. When Satoshi Nakamoto generated the first block in 2009, the mining difficulty was 1. At the time of writing, it amounts to about 20 trillion. If the difficulty in 2009 were as high as it is today, it would take Nakamoto millions of years to mine a new block.

Which is better – slow or fast?

There is no simple answer to which is better – a slow or fast block time. Some think that blockchains with slower block times are more secure, as it is harder to hack newly-created blocks. The deeper in the chain a block is, the harder it is to hack. Blockchains with faster block times are not insecure per se, it just takes more blocks to reach the level of security that a slower blockchain would have on a newly-created block.

Generally speaking, faster block times are more appropriate for applications for which it is important that information is added to the blockchain quickly. Slower block times, on the other hand, are more appropriate, for instance, when security is more important than speed.

Block times influence how long it takes to transfer cryptocurrencies. Bitcoin transactions take up to approximately 10 minutes, while ether (Ethereum) can be sent from one address to another in a matter of seconds. Based only on block time, Ethereum could therefore be described as handier for everyday purchases, such as buying a coffee, for instance. However, Bitcoin devs have always been aware of this limitation and have produced their own, layer 2, solutions.

As an investor trading in cryptocurrency through an international exchange, there is no need to worry about block time. That is the benefit of the exchange platform: it lets you enter the world of cryptocurrency investment without having to deal with the details. But the more you know about this game-changing currency system, the better situated you are to make good decisions. In cryptocurrency as in all things, knowledge is power.

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