Marine Rule of Twelfths Calculator
Show the seven integer-hour heights for a simplified six-hour rise or fall.
A QUICK WALKTHROUGH
How to use this tool
- Enter starting height, range, direction and a whole hour.
- Calculate the result.
- Copy the report or download it as TXT.
Formula and units
Height = start ± range × cumulative twelfths. Hours 0–6 use [0, 1, 3, 6, 9, 11, 12] / 12. Add for rise and subtract for fall. Range must be nonnegative; select an integer hour only.
Scope
This is a simplified arithmetic demonstration, not a location-specific tide prediction. It provides no fractional-hour interpolation, tide API or current estimate. Real tidal cycles vary; no safe-navigation recommendation is provided.
Local processing
Your entries stay in your browser. Copy and TXT export include the inputs, formula and scope.
GOOD TO KNOW
Common questions
How should I use the result?
Use it as an arithmetic estimate based on your supplied inputs.