Following a federal judge's decision that gay couples in Idaho can legally marry as of Friday, the number of states that allow same-sex marriage jumps to 19. But despite being fewer than half of the states, back-of-the-envelope calculations suggest that just about half of the U.S. gay population lives in a state that allows gay marriage. And if you consider states that have same-sex marriage decisions on hold, that percentage is poised to pass 60 percent.

Mike Chase kisses his partner Matthew Montoya on the steps of the Idaho Statehouse during a rally in support of same-sex marriage in Boise on May 13. (Kyle Green/The Idaho Statesman via AP)

This is an imprecise but revealing calculation that's worth walking through in detail. We start with the states that will allow same-sex marriages as of Friday. Here we introduce the (admittedly ugly) color scheme for the following graphs. Green means gay marriage is allowed. Red means it isn't. Yellow means that a same-sex marriage prohibition in the state has been overturned but put on hold pending appeal.

(You were warned that this was ugly.)

The tricky part is determining how many gay people live in each state. In February of last year, the Williams Institute at the University of California Los Angeles used census data to calculate the percentage of each state's population that identifies as gay. This is necessarily an estimate, and one that is subject to a lot of caveats. But it's the most rigorous estimate that we've seen. Here's the Williams Institute's map:

Via UCLA's Williams Institute.

If we then apply those percentages to the 2010 Census counts in each state, we get the following map. Darker blue means more gay residents (numbers have been rounded to the nearest thousand here; not quite respecting significant digits).

And then we compare the two maps: How many people live in each of the three categories of state.

The bar chart indicates the raw numbers. Per our estimate, just under 5 million gay Americans live in states in which they are not allowed to legally marry. About 4.6 million live in states where they can — about 43 percent. And in those in-limbo states, another million or so, mostly in Texas.

It probably doesn't bear mentioning (but we'll mention it anyway): In addition to these numbers being fairly rough estimates, the past few months have shown us that the legal status of any state could change at any time. So consider this data pertinent for the early afternoon of May 14, 2014. By tomorrow morning, who knows.