It's currently listed at 3,754m, but a new study puts it at just 3,724 m.
Capped by snow and ice, a 1991 avalanche (estimated to have contained 10 million cubic metres of snow and rock) undercut the mountain's brilliant crown by 10m (33ft). The avalanche left an overhang that later collapsed.
National School of Surveying researcher Pascal Sirguey: "As a result, the ice cap has been subject to erosion over the past 20 years."
A 2013 climbing expedition by the University of Otago revealed that Mt Cook is actually only 3,724m (12,217ft) high, cutting another 30m (98ft) off the mountain's height. And - voila! - the surveyors have lowered it by 30m.
Despite this, Mt Cook still towers above its close neighbour Mt Tasman which, at 3497m, is NZ's second-highest peak.
The stunning Mt Cook, which dominates the central Southern Alps, is a magnet for mountaineers from around the world, and has claimed well over 200 lives. It was first summited on Christmas Day 1894, by New Zealanders Tom Fyfe, James Clarke and George Graham.