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Tidal Height Converter

Master the rhythms of the sea. Convert tidal readings between metric and imperial systems and calculate heights relative to varying oceanic datums for safe passage.

CONVERTED TIDE HEIGHT
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Chart Datum Note

Total Depth = Charted Depth + Tide Height. Always ensure your tide height is positive unless specifically referencing a datum below the lowest tide.

Rule of Twelfths

A common rule of thumb for tidal flow estimating speed/height between high and low tide.

1st Hour: 1/12 height
2nd Hour: 2/12 height
3rd Hour: 3/12 height...

The Science of Tidal Measurement

Tidal height is the vertical distance between a specific reference plane (datum) and the surface of the water at any given time. For mariners, knowing this height is the difference between a successful voyage and running aground.

Reference Datums: CD vs. MSL

In maritime navigation, tidal height is rarely measured from the actual ocean floor. Instead, it is measured from the Chart Datum (CD), which is usually the level of the Lowest Astronomical Tide (LAT). Another common reference is Mean Sea Level (MSL), which is the average height of the ocean's surface. When you see a "tide table," the heights are almost always relative to the Chart Datum shown on your nautical chart.

The Importance of Unit Conversion

Because the shipping industry is global, mariners often transition between zones that use different standards. A pilot entering a port in the UK might work in meters, while an American vessel expects heights in feet. Errors in this conversion can be catastrophic. Our tool provides a high-precision bridge between these systems, including the necessary decimals for precise under-keel clearance (UKC) calculations.

Rule of Twelfths

Seafarers often use the "Rule of Twelfths" as a quick mental calculation for tidal height during the six-hour period between high and low tide. While our converter provides a static conversion of height values, understanding the rate of change in conjunction with height is essential for safe maneuvering in tidal reaches.

Solved Examples

Example 1: Under-Keel Clearance

Scenario: A chart indicates a depth of 5.0 meters at a specific rock. The tide table says the height is 1.5 meters. What is the total water depth in feet?

Step 1: Calculate total depth in meters: 5.0 + 1.5 = 6.5m.
Step 2: Convert to feet: 6.5 * 3.28084 = 21.325.
Final Result: 21.33 Feet

Frequently Asked Questions

What is Chart Datum (CD)?

Chart Datum is the level of water from which depths displayed on a nautical chart are measured. It is usually set to the Lowest Astronomical Tide (LAT) so that the actual depth is almost always greater than the charted depth.

How many types of tides are there?

Mainly three: Semidiurnal (two high and two low tides of similar height per day), Diurnal (one high and one low tide per day), and Mixed (varying heights).

What causes the tides?

Tides are primarily caused by the gravitational pull of the moon and the sun, combined with the Earth's rotation.