The Fee Ratio Multiple (FRM) was created by The Block’s analyst, Matteo Leibowitz, as a way to measure the security of a Proof-of-Work chain. The metric provides a framework to examine how secure chains will be once their block rewards disappear. In other words, how many multiples of the current transaction fees would be required to maintain a chain’s current level of security.
A low FRM suggests a chain can maintain its security level without relying on additional inflation of its native asset. A high FRM suggests that, unless transaction fees greatly increase, a chain will require high inflation of its block reward subsidies to maintain its security.