Guide

How to read a tide table

Four numbers a day, two of them high and two of them low — and one common misreading that catches people out.

The basic shape

Most New Zealand ports get roughly four tides a day: two highs and two lows, about 6 hours 12 minutes apart. The whole cycle runs about 24 hours 50 minutes, not 24 — which is why the tide is roughly 50 minutes later each day, and why some days show three tides instead of four.

The height is not the depth

This is the misreading that matters. A height of 3.1 m does not mean the water is 3.1 m deep. It means the water is 3.1 m above chart datum — a fixed reference set near the lowest tide ever expected. To get actual depth you add the tide height to the charted depth at that spot. More on chart datum →

Springs and neaps

Around new and full moon the sun and moon pull together and the range is large — spring tides, nothing to do with the season. Around the quarter moons they pull at angles and the range is small — neap tides. Spring lows are the lowest, which is why they are the ones worth knowing for reef walking and launching.

What the prediction cannot know

These are astronomical predictions: sun, moon and coastline. They do not include weather. A deep low and a strong onshore wind can raise the water well above the printed figure, and a big high can drop it below. In a storm the difference can exceed a metre. Never plan around a predicted height where being wrong would be dangerous.