The high performance sports agency said its target was to come home with at least 48 medals.
The 2008 Beijing Games saw Britain's best showing to date at an overseas Olympics with 47 medals -- the bottom of the current target range that has 79 as the best possible outcome.
No nation has ever followed up hosting a Summer Olympics with an even bigger medal tally at the subsequent Games and UK Sport's director of performance Simon Timson played down the likelihood of that happening.
"We set an aspirational target," he told reporters at a briefing, when asked about the post-2012 aim of winning more medals across more sports in Rio. "It was just that. It was based on something hugely ambitious."
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Timson said that a more evidence-based target was needed after assessing performances over the last two years.
"Let's not forget that 66 is still within range, and 79 is the top," he said. "If all the stars are aligned, it's possible that 66 could happen. It's not probable. We don't see it as a likely outcome."
Liz Nicholl, UK Sport's chief executive said more sports were targeting medals in Rio than in Beijing, with golf and rugby sevens now introduced to the programme and with the potential for top three performances.
Target ranges were produced for each sport, with cycling tipped to produce the most medals -- eight to 10 -- despite recent upheaval.
"Every sport hopes for a smooth run and cycling certainly experienced a few bumps in the road over the last few months," said UK Sport chairman Rod Carr.
"They've got very clear plans in place to be Rio-ready. We think they are executing them well and we've got great confidence that British cycling can deliver a lot of medals at both the Olympics and Paralympics."
British Cycling technical director Shane Sutton resigned in April after being suspended for allegedly making sexist and discriminatory remarks about rider Jess Varnish and, separately, para-cyclists.
Athletics, with the 2012 golden trio of Mo Farah, Jessica Ennis-Hill and Greg Rutherford returning for Rio, was targeting seven to nine medals while rowing was expected to reap six to eight.
The Paralympic target was 121 medals.
(Reporting by Alan Baldwin, editing by Pritha Sarkar)
