Tidal Range Calculator
Calculate tidal range, high and low tide times, and current strength estimates. Plan sailing and anchoring around tidal conditions.
Specialist tool for Sailing1 documented formulaFocused single-task workflowPrivate in your browser
Use this result well
A quick decision brief for this specific tool
Inputs that matter
High Tide Height, Low Tide Height, Hours After Low Tide, Tidal Period
Output to expect
Tidal Range Calculator
How it works
1 documented formula across 1 calculation mode
- Keep 3 bounded inputs within the limits shown beside the fields.
- Confirm that every value uses the unit and time basis shown before comparing scenarios.
- Change one input at a time to see which assumption materially changes the result.
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Reference & details
How it works
Updated July 2026
How it works
Updated July 2026Tidal Range
Tidal range is the vertical difference between high and low tide. Spring tides (full/new moon) produce maximum range; neap tides (quarter moon) produce minimum.
Range = MHW − MLW (mean high − mean low water)Tide Height at Time
Tidal height follows sinusoidal harmonic components (M2, S2, K1, O1). Simplified: interpolate between known high and low times using rule of twelfths for planning.
Rule of twelfths: 1/12, 2/12, 3/12, 3/12, 2/12, 1/12 per hour of 6-hour tide phaseTidal Current Estimation
Maximum current occurs mid-tide. Peak speed correlates with range and channel geometry. Spring tides produce roughly 1.5× neap current in many locations.
Current max ∝ tidal range × channel constriction factorUpdated: July 2026
Example Scenarios
Low tide 2 m depth at datum; high tide adds 3 m = 5 m depth. At 7:1 scope, rode need varies 21 m (low) vs 35 m (high) — set anchor for low tide depth.
Bridge 12 m clearance at MHW. Vessel air draft 10 m with 1.5 m spring tide above MHW: 12 − 1.5 = 10.5 m — passes with 0.5 m margin. Check tide table for exact hour.
Channel max flood 2 knots at 2 hours after low tide. Depart 1 hour before for slack-to-flood transition, riding favorable current through narrow pass.
Common Mistakes to Avoid
Common Mistakes to Avoid
Anchoring for high tide depth only
At low tide, insufficient depth grounds the boat or steepens rode angle until anchor breaks free. Always plan scope and depth at lowest astronomical tide.
Using tide time from a distant station without correction
Secondary ports may differ 30+ minutes and different range from reference station. Apply local corrections from tidal almanac or chart.
FAQ
Approximates tide height change per hour: in a 6-hour rise, water rises 1/12 of range in hour 1, 2/12 in hour 2, 3/12 in hours 3–4, then decreasing. Useful without full harmonic data.
Spring tides occur at new and full moon when sun and moon align — largest range. Neap tides at quarter moon when forces partially cancel — smallest range.
Use official tide tables (NOAA in US, UKHO in Britain) for reference stations. Apply time and height corrections from almanac for secondary ports.
Yes. Calculate scope at lowest expected tide depth — the shallowest point determines maximum rode angle and holding. High tide adds depth margin only.
Typically midway between high and low tide at most locations. Slack water occurs near high and low tide when current reverses direction.
About Tidal Range Calculator
Tides affect anchoring depth, bridge clearance, and current strength. This calculator estimates tidal range from harmonic constituents or reference station data, and predicts high/low times for voyage planning.