The victory completed a 5-0 sweep in the series following a 2-0 win in the Test series.
Previous best
Ronchi's 64 off 29 balls - including six sixes and five fours - helped Australia amass 341 for eight off 50 overs, bettering their previous best against the West Indies of 338 for six in Melbourne in 2001.
David Hussey scored a 19-ball half-century in the latter stages, hitting four fours and four sixes in 52 off 21 balls, after Andrew Symonds (66) and Mike Hussey (51) added more measured half-centuries to anchor the middle innings.
The West Indies never challenged the target and were bowled out for 172 off 39.5 overs.
Shawn Findlay, in only his second one-dayer, top-scored with an unbeaten 59.
Left-arm pacer Johnson claimed two early wickets and then returned to decimate the tail end to finish with five for 29 off 7.5 overs.
Australia began well after winning the toss on another fine batting pitch.
Openers Shaun Marsh (49) and Shane Watson (29) combined for 70 off 12.5 overs.
After Watson departed with a square cut to third man off Dwayne Bravo, Ronchi entered in only his second one-day innings and hit Chris Gayle for three sixes in one over.
He also punished Edwards and reached his half-century off 22 balls to equal the second-fastest by an Australian.
Second wicket
Marsh and Ronchi added another 59 runs for the second wicket, but the West Indian bowlers struck back and claimed three wickets for 13 runs. Marsh edged Edwards to wicketkeeper Denesh Ramdin and the spin of Nikita Miller, and Ramnaresh Sarwan accounted for Ronchi and captain Michael Clarke to reduce the Australians to 152 for four in the 23rd over.
Ronchi snicked left-arm spinner Miller's first ball to Ramdin, who also claimed Clarke from Sarwan's first delivery.
Symonds and Michael Hussey then joined to reclaim the momentum for Australia, sharing a stand of 113 for the fifth wicket.
Symonds struck six fours and a six off 80 balls before he edged to Ramdin.
Hussey hit three fours off 56 deliveries in his 51.
fastest half-century
David Hussey appeared on course for the fastest half-century by an Australian, but fell just short of Simon O'Donnell's 18-ball effort in 1999 against Sri Lanka in Sharjah.
Johnson quickly stamped Australia's dominance as West Indies replied meekly.
He claimed Gayle and Sarwan to leave the home team tottering at 21 for two.
Gayle edged to wicketkeeper Ronchi while Sarwan miscued to mid-off.
Veteran Shivnarine Chanderpaul and Findlay were the only players to offer much resistance.
Chanderpaul hit 38 off 49 balls but he fell to Clarke's left-arm spin after striking four fours.
Clarke also added the wicket of Andre Fletcher, stumped by Ronchi off a leg-side wide.
Symonds also picked up two wickets in the middle order before Johnson returned to swiftly end the match.
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