'Tāne Mahuta (Lord of the Forest) is historically New Zealand’s largest known living kauri tree and without doubt its most famous. Insofar as Champion trees points are concerned, Tāne Mahuta comes second to Te Matua Ngahere. It is thought this tree was first discovered and identified in the 1920’s when contracted surveyors surveyed the present State Highway 12 through the forest. In 1928 Nicholas Yakas and other Bushmen, which were building the road, also identified the big tree Tāne Mahuta.'
'According to Maori mythology Tane is the son of Ranginui the sky father and Papatuanuku the earth mother. Tane was the child that tore his parent’s parental embrace and once done set about clothing his mother in the forest we have here today. All living creatures of the forest are regarded as Tāne’s children.'
Ref, Department of Conservation, Tāne Mahuta Track notes.

'In 2002, it was laser measured at 45.2 m tall with a dbh of 491 cm; that number is misleading, though, because the base of the tree is buttressed. The main trunk is 17.8 m tall and contains 255 m3 of wood. The total wood volume, including the crown, is much larger. The enormous crown is nearly 35 m wide and has a dozen branches over 1 m in diameter, three greater than 2 m, and one over 3 m. Adding the wood in the crown brings the total wood volume up to 516.7 m3, making this tree just a bit larger than the largest known Thuja plicata. Thus Agathis australis is the largest tree in the Araucariaceae and the third largest conifer, after Sequoiadendron and Sequoia (Robert Van Pelt e-mail, 27-Jan-2003).' Source: www.conifers.org

'The often quoted height (51.5 m) volume (244.5 m3) and diameter (438 cm) of Tāne Mahuta is taken from Burstall and Sale's 1984 book 'Great Trees of New Zealand. The calculations were made using forestry methodology of the time and were sourced from a 1971 New Zealand Forest Service survey of 13, and later 20, named kauri in Waipoua and Omahuta Forests. The volumes established for each tree were of merchantable timber volumes inside bark. The 2002 measurements quoted on this record are taken from visiting U.S.A. tree researcher Robert Van Pelt's calculations where he used very accurate laser based technology and tree measurement methodology.' (Cadwallader 2011).

References:
[1] Burstall, S.W. NZFS, Forest Research Institute, Mensuration Report No. 16, 1971 (unpublished).
[2] Burstall S.W. & Sale E.V. 'Great Trees of New Zealand' 1984.
[3] Robert Van Pelt 2002 & 2009 NZ Summary spreadsheet.