How to Read a Tide Chart: A Beginner's Complete Guide

By TideTimes Global·March 20, 2025·Updated March 20, 2025

⚡ Quick Answer

A tide chart shows the predicted height of water at a specific location over time. The curve rises to a peak (high tide) and falls to a trough (low tide) roughly twice each day. Heights are measured from Chart Datum — the lowest reference point. To use a tide chart: find today's date, read the listed high and low tide times, and note the heights in meters to understand how much water will be present.

What Is a Tide Chart?

A tide chart (or tide table) is a prediction of water height at a specific coastal location over a period of days. It tells you two critical things: when the water will be at its highest and lowest points, and how high or low those extremes will be.

Tide charts are generated by analyzing astronomical patterns — primarily the gravitational pull of the Moon and Sun — and applying them to the known tidal behavior of a specific location. They are remarkably accurate: predictions are typically within a few minutes and centimeters of actual conditions, assuming normal weather.

Reading the Numbers: Times and Heights

Every entry in a tide table contains two numbers: a time and a height.

Time is when the tide reaches its high or low point. This is given in local time for the station's timezone. Be careful with daylight saving — tide tables in some regions do not automatically adjust.

Height is the water level above Chart Datum, measured in metres. A high tide of 2.4m means the water surface is 2.4 metres above the baseline. A low tide of 0.1m means only 10 centimetres of water above that same baseline — very shallow conditions.

What Is Chart Datum?

Chart Datum is the reference level from which all tide heights are measured. It is set to approximately the lowest astronomical tide (LAT) — the lowest level the tide is ever predicted to reach under normal conditions.

This means tide heights shown on a chart are always positive (or zero). A height of 0.0m doesn't mean dry land — it means the water is at its theoretical minimum level. The actual depth at any point also depends on the natural depth of the seabed at that location.

For practical use: a higher Chart Datum number = more water = safer for navigation and beach activities. A lower number = less water = better for beachcombing and tide pooling.

Understanding the Tide Curve Graph

Modern tide charts like those on TideTimes Global show a smooth curve — not just discrete high/low entries. This curve shows the predicted water height at every hour of the day.

The smooth S-curve between tides follows a pattern called the Rule of Twelfths: the tide moves slowly near its high and low points, then accelerates rapidly through the middle range. In the first hour after low tide, water rises by only 1/12 of the total range. By the third and fourth hours, it's rising at 3/12 per hour — the fastest point. It slows again in the final hours before high tide.

This matters practically: if you're watching the tide come in from a rock platform, the middle hours are when water rises fastest and can catch you off guard.

Tidal Range: The Difference Between High and Low

Tidal range is simply the difference between today's high tide height and low tide height. A high of 2.8m and a low of 0.3m gives a range of 2.5m.

Tidal range varies dramatically by location. Some areas experience tidal ranges of less than 0.5m (microtidal), while others like the Bay of Fundy in Canada can exceed 16m. The range also changes through the monthly lunar cycle: spring tides (near new and full moon) have larger ranges, while neap tides (near quarter moons) have smaller ranges.

Large tidal ranges create stronger currents, more exposed beach at low tide, and more dramatic changes in conditions.

💬 People Also Ask

How many high tides are there per day?

Most coastal locations experience two high tides and two low tides per day — a pattern called semidiurnal. However, some locations (particularly along the Gulf of Mexico and parts of Southeast Asia) experience only one high and one low tide per day (diurnal). A few locations have a mixed pattern with two unequal highs and two unequal lows.

Why are tide times different every day?

The Moon rises approximately 50 minutes later each day as it orbits Earth. Since tides are primarily driven by the Moon's gravitational pull, each subsequent tide also occurs roughly 50 minutes later. Over a month, this shift cycles through a full 24 hours, which is why the same tide time recurs roughly once per month.

Are tide predictions always accurate?

Tide predictions are highly accurate under normal conditions — typically within minutes and a few centimeters. The main sources of error are weather: strong sustained onshore winds can push extra water into coastal areas (storm surge), raising actual water levels above predictions. Offshore winds can have the opposite effect. Always allow a safety margin in weather-affected conditions.

What is a neap tide vs spring tide on a tide chart?

On a tide chart, spring tides appear as days with a large difference between high and low water heights (large tidal range). Neap tides show as days with a smaller difference. Spring tides occur around new and full moon; neap tides around first and third quarter moon. You can identify them visually on a monthly chart as alternating peaks of high-range and low-range tidal cycles.

🧭 Expert Tips

Always check the timezone noted on the tide table. Many travellers get caught out by tide tables that use standard time while the local area has shifted to daylight saving.
The tide chart shows astronomical predictions only. In practice, a strong storm can raise water levels by 0.5–2m above prediction (storm surge). Never rely solely on tide tables in severe weather.
Heights below 0.5m at low tide are excellent for rock pooling and exploring tidal flats — these are the lowest exposures of the month. Check your tide chart for the lowest lows, which cluster around spring tides.
When fishing or boating, note not just the high and low times but also the rate of change. A 2m range compressed into 6 hours produces much stronger currents than the same range over 12 hours.

← Back to: Understanding Tides: Complete Guide