What is the rule of twelfths?

The rule of twelfths is a method to estimate tide height at any point between high and low water. It divides the tidal range into 12 equal parts and distributes them over 6 hours: 1/12 in hour 1, 2/12 in hour 2, 3/12 in hours 3 and 4, 2/12 in hour 5, and 1/12 in hour 6. The fastest rise/fall occurs in hours 3 and 4 (mid-tide).

How accurate is the rule of twelfths?

The rule of twelfths assumes a sinusoidal tidal curve and a 6-hour tide cycle, which is a reasonable approximation for most UK semidiurnal tides. However, it is less accurate in areas with significant tidal asymmetry, river estuaries, or where the tidal cycle differs from 6 hours. Always cross-check with official tide tables.

When are tidal currents strongest?

Tidal currents are strongest at mid-tide (hours 3 and 4), when the water is rising or falling at its fastest rate. This is when the most water is moving. Slack water (minimal current) occurs near high water and low water. Spring tides have stronger currents than neap tides.

Where can I find UK tide times?

The UK Hydrographic Office (UKHO) publishes official tide tables. The BBC Weather website has tide times for major UK ports. The Admiralty EasyTide service provides free predictions for UK ports. For sea kayaking, the Imray and Reeds almanacs are popular references.

CampCalcs

Tide Calculator

Estimate tide heights using the rule of twelfths for coastal trip planning.

High Tide Height

Height above chart datum

Low Tide Height

Hours After High Water

Tidal Type

How We Calculate This

Rule of Twelfths

The tidal range is divided into 12 parts, distributed over 6 hours as: 1, 2, 3, 3, 2, 1

One-twelfth = (High tide - Low tide) / 12

Hour 1: falls 1/12, Hour 2: falls 2/12, Hour 3: falls 3/12, Hour 4: falls 3/12, Hour 5: falls 2/12, Hour 6: falls 1/12

This gives the height at any time between high and low water.

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Last updated: February 2026

All calculations are estimates. Always verify conditions and use proper safety equipment outdoors.