Update: estimates for the 2012-13 season are available here.
Nielsen TV ratings are merely percentages of whatever is being measured. Sometimes it gets confusing because so many different things are measured.
If you see a 3.4 national adults 18-49 rating, that doesn't mean 3.4 million adults 18-49, it just means 3.4 percent of the 127,860,000 adults 18-49 in the United States (down from 131,490,000 last season) who live in a household with a television were watching based on the Nielsen estimates for the 2011-12 television season.
So a 3.4 adults 18-49 rating works out to be around 4.35 million adults 18-49.
Here are some of the ratings slices we frequently post data for and the total size of the populations being measured.
Numbers below were for the 2011-12 season: (estimates for the 2012-13 season are available here).
|Nielsen Estimates*||Population||A 1.0Equals|
|Households||114.7 Million||1.147 Million|
|Adults 18-49||127.86 Million||1.279 Million|
|Women 18-49||64.02 Million||640,200|
|Men 18-49||63.84 Million||638,400|
|Adults 18-34||67.59 Million||675,900|
|Women 18-34||33.55 Million||335,500|
|Men 18-34||34.04 Million||340,400|
|Adults 25-54||120.68 Million||1.207 Million|
|Teens 12-17||24.04 Million||240,400|
|Kids 2-11||41.18 Million||411,800|
I didn't add it to the list above, but there are 289.70 million (down from 294.65 last season) potential "total viewers" in the U.S. age 2+ in households with TVs according to the estimates for the 2011-12 season.