The first thing to be said about lengths of coastline is that it very much depends on how you measure it.
I found two sources (Wikipedia and Statista) that rank the states according to the same two measures. Wikipedia defines them as the CRS (Congressional Research Services) method and the NOAA (National Oceanic and Atmospheric Administration) method, while Statista refers to them as "general coastline" and "tidal shoreline". Either way, Alaska has the longest coastline and Florida has the second longest; but if you go any further (third longest, and so on) the two methods give different rankings.
I'm not convinced that Statista is using the terms "coastline" and "shoreline" scientifically. In trying to nail down the difference, I came across this on a website called Springer Link (apparently a collection of scientific papers): "The term coastline is generally used to describe the approximate boundaries at relatively large spatial scales. Shoreline is used to describe the precise location of the boundary between land and water."
According to Wikipedia, however, the difference between the two measures (both of which Wikipedia refers to as "coastline") is more to do with whether you include coastal inlets and freshwater lakes. Wikipedia also refers to the "coastline paradox", which is essentially that the more accurately you measure it, the longer it gets.
In the case of the coastlines and shorelines of the fifty US states, the difference between the two measures described above is striking. Alaska's is by far the longest according to either measure, with 6,640 miles of coastline according to the CRS method – more than all the others put together – and 33,904 miles by the NOAA method. Hawaii, which you might have expected to come second, is fourth in the CRS ranking but only 18th in the NOAA's.
As already mentioned, Florida has the second longest coastline (1,350 miles and 8,426 miles respectively), but then it starts to vary. According to the CRS, California has the third longest (840 miles), but according to the NOAA it's Louisiana (7,721 miles). Fourth longest by the NOAA method is Maine (3,478 miles), and California is fifth (3,427 miles).
To summarise, here are the five states with the longest coastlines, by each of the two methods.
CRS: Alaska (6,640 miles), Florida (1.350), California (840), Hawaii (397), Texas (367).
NOAA: Alaska (33,904 miles), Florida (8,436), Louisiana (7,721), Maine (3,478), California (3,427).
According to Wikipedia, Alaska has slightly over half of the total US coastline by the CRS method but slightly less than a third (i.e. half as much as the other states put together) by the NOAA.
© Haydn Thompson 2023