Famously private, Hart, who is married with two children, hasn't given an interview to the New Zealand press in about a decade.
Hart is the second wealthiest person in Australasia. Mining tycoon Gina Rinehart is the richest, ranking at No 69 on the Forbes list with a wealth estimated at $15b.
He is richer than entrepreneur Richard Branson, who is ranked No 324 and worth $5b.
New Zealand's second-richest man, Richard Chandler, was ranked at No 1098.
Chandler is worth $1.91b, a drop from $2.45b last year.
For the fourth time in a row, Bill Gates was named as the richest man in the world, with an estimated fortune of $86b and Warren Buffett came in at second place with a net worth of $75.6b.
Amazon's chief executive Jeff Bezos came in third place, with $72b, up from $27b the previous year, making him the biggest wealth gainer on the list.
He was followed by Zara boss Amancio Ortega with $71.3b, and then Facebook founder Mark Zuckerberg in fifth place with an estimated worth of $69.1b.
Donald Trump's fortune has fallen by an estimated $200 million since he took office, according to Forbes magazine, plunging him more than 200 rungs down the worldwide wealth rankings.
Trump was ranked at No 544, with a net worth of around $3.5 billion.
