Tide Calculator

The Rule of Twelfths estimates tide height between high and low tide. The tidal range is divided into 12 parts. In the first hour, the tide changes 1/12. In hours 2: 2/12, hours 3: 3/12, hour 4: 3/12, hour 5: 2/12, hour 6: 1/12. The tide moves fastest in the middle 2 hours.

Tides are caused primarily by the gravitational pull of the Moon and Sun on Earth's oceans. The Moon has the stronger effect due to proximity. Spring tides (highest tides) occur when the Sun and Moon align (new and full moon). Neap tides (lowest tides) occur at quarter moons.

Most coastlines have semidiurnal tides: 2 high tides and 2 low tides per day, approximately 12 hours 25 minutes apart. The Gulf of Mexico has diurnal tides (1 high, 1 low per day). The Pacific Coast has mixed tides with unequal highs and lows.