More than 13 million US households with televisions are not prepared for the transition to all digital broadcasting on 18 February 2009.
Market research firm Nielsen said that a further six million households have at least one television that will no longer work after that date.
Nielsen found that 10.1 per cent of all US households will have no access to television signals if the transition occurred today.
Around 16.8 per cent of all households have at least one analogue television that would not work after the switch.
New York is the most ready local television market with just 3.5 per cent of "unready" televisions in the area.
Portland, Oregon is the least prepared local market with 22.4 per cent of all households using only analogue sets and over-the-air television.
"The change to all-digital broadcasting is the most significant change in the history of television," said Eric Rossi, senior manager for product leadership and leader of Nielsen's digital transition preparedness team.
"Unlike other advances such as colour, older television sets will no longer be able to receive television signals without a converter.
"Over the past 18 months we have been reviewing every aspect of the digital transition to measure the impact and help clients understand where things stand as we all prepare for the challenges."
Nielsen found that adults over 55 are better prepared than younger citizens, and that whites and Asians are more ready than other ethnic groups.
More Hispanic households still rely on analogue over-the-air broadcast television than non-Hispanics.
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