What Is the Relationship between the Cost of a 51% Attack and the Market Capitalization of a Cryptocurrency?

The cost of a 51% attack is generally positively correlated with the market capitalization of a cryptocurrency. A higher market cap usually implies a more robust and larger network with a higher total hash rate, making the required computing power and therefore the cost of the attack prohibitively expensive.

The cost is often calculated as the hourly cost to rent the necessary hash power to sustain the attack.