What is a tide?
9 min read
What a tide is, why the sea rises and falls twice a day at most coasts, and why your beach does not behave like the one 50 km away.
Tide guides
Plain explanations of the numbers this site prints — what a tide is, why some days are bigger than others, and how to read a station page like someone who has done it for years.
Understanding the tides
How does the Moon affect the tides?
9 min read
The Moon raises the tide by pulling unevenly on the Earth. What its phase, its distance and its angle above the equator each change, and by how much.
Spring tides and neap tides
10 min read
Spring tides and neap tides are the fortnightly swing between the month’s biggest tides and its smallest: what causes each, when they fall, and how to spot them.
King tides
9 min read
King tides are the highest predicted tides of the year: a spring tide at lunar perigee. What makes one, when they fall, and what they do to a coast.
Types of tides: diurnal, semidiurnal and mixed
8 min read
The three types of tides — semidiurnal, diurnal and mixed: what each looks like on a chart, which coasts have which, and why it changes how you read a table.
What is tidal range?
8 min read
What tidal range means, how to work it out from two rows of a tide table, and why the same Moon gives one coast half a metre and another sixteen.
How long does high tide last?
8 min read
How long high tide lasts, how many high tides a day you get, and how long the water takes to fall to the next low.
Do lakes have tides?
7 min read
Whether lakes have tides, why the Great Lakes’ tide is under five centimetres, and what a seiche is — the thing people actually see.
Reading this site
How to read a tide chart
9 min read
How to read a tide chart: what the rows and the heights mean, how to work out the level between them, and the mistakes that catch people out.
Understanding tidal coefficients
8 min read
The 20–120 number beside every day on this site: what it measures, what the bands mean, and why it is the fastest way to pick a day.
What is chart datum?
7 min read
The zero line every tide height is measured from — why it differs between countries, why our heights can go negative, and what that means when you read a depth.
How solunar theory works
6 min read
Major and minor periods, where they come from, what the evidence for them actually is, and how we compute the ones on your station page.
Gauge vs. interpolated stations
7 min read
Two kinds of station, two levels of confidence — how to tell them apart on this site and how much to trust each one.
See it on your coast
Every idea in these guides is a number on a station page — tide times, coefficient, solunar windows and the badge that says how the prediction was made.