Three-quarters saw Wales win Grand Slam decider.
The survey, commissioned by BBC Cymru Wales, also showed a further 300,000 watched the match in a bar, pub or rugby club. And another 400,000 saw some coverage of the game on television later during the weekend.
The findings were revealed in a survey carried out by Beaufort Research, which also revealed 76% of all adults in Wales saw at least some of the match over the weekend.
Unsurprisingly, interest in the final match of the tournament was huge, with 86% of adults in Wales said to be interested in the result, rising to 92% of men.
And 84% said it was important to them that the BBC provides full coverage of the Six Nations.
Richard Thomas, BBC Cymru Wales' head of marketing, communications and audiences, said: "We know that the audience's appetite for rugby in Wales is massive, but these figures show just how passionate the people of Wales are about their rugby."
The Six Nations had record average audiences in Wales of 800,000 across Wales' five matches and the average audience during the final periods of Wales' five matches were the highest ever.
The audience peaked at a million viewers for two of the games - the highest TV audience in Wales on any channel for two years.
BBC One Wales' five highest audiences of 2012 so far in Wales have occurred during Wales five matches in the Six Nations.