Tide Height Estimator

Summary

Enter high and low tide data to estimate water depth at any point in the tidal cycle using the Rule of Twelfths.

How it works

1. Enter the time and height of the preceding high tide.
2. Enter the time and height of the following low tide (or vice versa).
3. Enter the time at which you want to know the estimated water depth.
4. The tool calculates elapsed time, determines which twelfth-hour segment applies, and sums the proportional rise or fall.
5. The result shows estimated height above chart datum and the current tidal state (flooding, ebbing, or slack).

Use cases

• Check minimum depth under keel before navigating a shallow bar or channel.
• Plan the best window to cross a tidal estuary at safe water depth.
• Estimate anchor rode scope by knowing the maximum tide height overnight.
• Teach trainees the Rule of Twelfths with an interactive worked example.
• Verify whether a boat will remain afloat at low tide when left on a drying mooring.
• Cross-check tide table predictions against a quick mental arithmetic method.

Frequently Asked Questions