How to Read a Tide Table: Times, Heights and Chart Datum Without Guesswork
A tide table packs a lot of precision into a small grid: for every day it lists the times the water will turn, and how high or low it will stand. Read it correctly and you know when the rocks you want to fish from will be knee-deep, or when the reef flat you want to photograph will be exposed. Misread it and you get wet boots at best — cut off by the returning sea at worst. Here is the whole skill, in one page.
Key takeaways
- Each row gives the day's high and low waters as a time plus a height; times on this site are always UTC+8.
- Heights are metres above chart datum — zero is roughly the lowest low water ever expected, not the sand.
- The range (high minus low) tells you how far the water will move that day.
- Events belong to their date: a 00:32 high on the 17th is just after midnight, hours after the 16th's entries.
- Tide tables are astronomical predictions; wind and pressure shift real levels — check warnings too.
The two numbers on every event
Open any of our tables — Quarry Bay is a good example — and each day shows up to four events: high water (H) and low water (L), alternating through the day. Each event carries a time and a height. The time is when the water stops rising or falling — the turn — and the height says how far the surface will sit above chart datum at that moment. Between events the level moves smoothly; halfway between a high and the next low, the water is usually moving fastest.
What "above chart datum" actually means
Chart datum is the zero plane used on nautical charts, chosen to sit near the lowest astronomical tide — so almost all predicted heights come out positive. On this site every table, Hong Kong and Taiwan alike, uses metres above chart datum, which is also what the official sources publish. Two practical consequences follow. First, a bigger number always means deeper water, so you can compare days directly. Second, the number is not the depth at your feet: it does not know whether your reef is 0.3 m or 3 m below datum. Local depth comes from the place itself; the table tells you how the water above it moves. Taiwan's official annual tables also list heights against local mean sea level — interesting for engineers, but chart datum is the anglers' and walkers' standard.
Ranges, and why some days have fewer entries
Subtract the day's lowest low from its highest high and you get the range — the single most useful number for planning. Big ranges (spring tides) mean fast currents, more exposed reef at low, and a faster return of the water; small ranges (neap tides) mean quieter, shallower movement. The background to that cycle is in how tides work.
Do not panic when a day shows only two or even one event, as happens at Keelung or around neaps at Kaohsiung. In mixed-tide regimes the "missing" high or low is real but so small that the official table folds it into the neighbours, or it falls a few minutes across midnight onto the adjacent date. The water still rose and fell — just gently.
Three mistakes that catch people out
- Reading the wrong day's midnight. A high at 00:32 on the 17th happens a few minutes after the 17th begins — hours after the 16th's last low. When planning across dusk or dawn, always read two days of rows.
- Assuming the table knows the weather. A strong monsoon or a distant typhoon can pile water half a metre above prediction — or pull it below. The astronomical table is the baseline, the warnings are the correction.
- Planning the low, ignoring the rise. The lowest tide is the moment of maximum exposure, but it is also the moment the sea starts coming back. If your route home crosses a flat or a cutting, plan to leave on the falling tide — the full picture is in our beach-safety guide.
Using the finder instead of squinting
Every location page on this site includes a low-tide window finder: choose a threshold — say 1.00 m — and it lists the next windows when the predicted water stays at or below it, straight from the same official baked data. That answers the real question most people have ("when can I wade / photograph / dig?") without doing the subtraction yourself. Try it on Quarry Bay or Taichung Port.
Predictions, not promises
Our tables are baked from official Hong Kong Observatory and Taiwan Central Weather Administration predictions, stamped with source and retrieval date on every page. They are astronomical estimates: actual conditions vary, and neither we nor the official sources guarantee water levels. For anything safety-critical, confirm against the official live pages linked on each table.