In general, the songwriter gets a standard ASCAP payment for each copy of the song sold. I can’t find the exact figure, but it’s a few cents a copy per song. Thus your base payment is determined by the number of sales of the album as a whole.
You also get a payment for performances – live, radio, etc. – according to this formula. Thus, if your song gets radio airplay, you get paid more money.
This assumes you haven’t sold the song outright and gave the rights to someone else. The system is set up so the songwriter can share in the success of the song.
From the FAQ on the Harry Fox Agency website:
What is the current statutory mechanical rate for physical product (ex. CDs, Cassettes and Vinyl), PDDs, and ringtones? How is it calculated?**
The current statutory mechanical royalty rate is $.091 (9.1 cents) per song per unit for recordings of compositions up to five minutes (5:00) in length.
For example, if one were to make a recording of a song that is less than five minutes in length (e.g. 4:07) and then manufacture and distribute 500 units of the recording, the total amount of royalties due would be $45.50. ($0.091 X 500 (units) = $45.50).
For songs over five minutes in length, the rate is based upon $.0175 (1.75 cents) per minute or fraction thereof as demonstrated below:
5:01 to 6:00 = 0.105 (6 X .0175)
6:01 to 7:00 = 0.1225 (7 X .0175)
7:01 to 8:00 = 0.14 (8 X .0175)
For example, if one were to make a recording of a song that is six minutes and thirty-eight seconds in length (6:38) and then manufacture and distribute 500 units, the total amount of royalties due is $56.25. ($0.1225 X 500 (units) = $61.25).
The current statutory rate for ringtones is $0.24 (24 cents) per song per unit.
So, just under a dime a dance. $91,000 for a million seller. That’s just for the songwriting. As RealityChuck pointed out, there are other sources of income, but the lion’s share is the mechanical copyright.
The move away from albums is a Bad Thing for songwriters, who would get to piggy-back on the success of an album with one hit song on it.
A classic example: new wave vet Nick Lowe made more than a million dollars thanks to Curtis Stiger’s cover of “(What’s So Funny 'Bout) Peace, Love and Understanding” being included on the soundtrack album for “The Bodyguard.”
Handsomeharry, you asked specifically about one song on one album, and the airplays thereof. But behind such questions are often greater questions such as “how much does a songwriter or performer make?” which is a different question.
The income from one song on one album may be dwarfed by related income. Others may perform it, record it, it may be incorporated into movies, advertising, toys (!), mashups, etc. There are many other *potential *sources of income than just the album sales and airplay. Not to mention you, as a writer, may have an easier time of getting other material you created into a profit-making mode once you have crossed the first hurdle.
And sometimes income comes from unexpected sources. A friend of mine had a minor hit song in the US, but a year later, he started getting royalties from Brazil, where the song had become a much greater hit. And no, it wasn’t in Portuguese, so go figure.