AHD (Australian Height Datum)
AHD (Australian Height Datum) is Australia's official vertical datum, referenced to mean sea level. Used for flood levels, finished floor levels, and construction surveys
Ask Chalkline about this →AHD stands for Australian Height Datum. It is the official national vertical datum for Australia, adopted in 1971 by the National Mapping Council. AHD is referenced to the mean sea level of 32 tide gauge sites measured around the Australian coastline between 1966 and 1968. A point at RL 0.000 m AHD is effectively at mean sea level; all heights in Australia are expressed as metres above or below that reference.
In residential construction, AHD matters because council consent conditions and flood planning instruments commonly set minimum finished floor levels (FFL) in metres AHD. If a site is in a flood-affected zone, the certifier will require the surveyor to reference the TBM (temporary benchmark) to AHD, not to an assumed local datum.
Also known as: AHD71 (the original 1971 adjustment).
Category: Surveying and levels.
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Last updated: 2026-05-10. Verified: 2026-05-10. Quarterly review for currency.