How is tide height measured?

Tide height is the predicted height of the sea at a particular time in the tidal cycle. It is normally expressed in metres.

Tide heights are measured against a defined reference level, known as a tidal datum. This allows predicted water levels to be described consistently for a particular location.

For example, if a tide prediction shows a high tide height of 4.5 metres, this represents the predicted sea level relative to the tidal datum used for that location.

The actual sea level can be higher or lower than the predicted height because weather conditions, including wind and atmospheric pressure, can affect coastal water levels.