Tide range calculator
The tidal range is the vertical difference between high water and low water at a coastal location, and it is one of the most practical numbers in navigation, harbor operations, fishing and coastal engineering. This calculator takes the height of high water and the height of low water, measured against the same chart datum, and returns two figures. The tidal range is simply the high water height minus the low water height, the total rise and fall of the sea over the tidal cycle. The mean tide level is the average of the two heights, the midpoint about which the water oscillates. Tidal range varies enormously around the world, from a few centimeters in nearly tideless seas to over fifteen meters in places like the Bay of Fundy, and it changes through the month: largest at spring tides near the new and full moon, smallest at neap tides near the quarter moons. Knowing the range tells a mariner how much water will be under the keel. Enter your own high and low water heights to plan a passage, size a structure or check an exercise. Every figure here is computed deterministically from the heights you provide, shown below with a worked example that reconciles exactly to the calculator.
The tidal range is high water minus low water and the mean tide level is their average. With a high water of 2.4 m and a low water of 0.3 m, the tidal range is 2.10 m and the mean tide level is 1.35 m.
Tidal range and mean level
tidal range = high water height - low water height
mean tide level = ( high water + low water ) / 2
heights measured against the same chart datum
range is largest at springs, smallest at neaps
The tidal range is the full vertical travel of the water between a high and the adjacent low, found by subtracting the two heights. The mean tide level is the midpoint they swing around, the simple average of the high and low water heights.
Worked example
A tide reaches a high water of 2.4 m and falls to a low water of 0.3 m on the same datum.
- Tidal range = 2.4 - 0.3 = 2.1 m
- Sum of heights = 2.4 + 0.3 = 2.7 m
- Mean tide level = 2.7 / 2 = 1.35 m
- The water rises and falls 2.10 m about a midpoint of 1.35 m
The tidal range is 2.10 m and the mean tide level is 1.35 m. These are the calculator's default inputs, so the results above match the widget exactly.
Typical tidal range categories
| Category | Approximate range |
|---|---|
| Microtidal | Less than 2 m |
| Mesotidal | 2 m to 4 m |
| Macrotidal | Greater than 4 m |
Categories follow the common coastal classification by tidal range.
Tide range calculator: frequently asked questions
What is tidal range?
Tidal range is the vertical difference in sea level between high water and the adjacent low water at a location. It is the total amount the sea rises and falls over one tidal cycle. A large range means a big difference between high and low tide; a small range means the water barely moves vertically.
What is mean tide level?
Mean tide level is the average of the high water and low water heights, the midpoint about which the tide oscillates. It is a simple two-point average and differs slightly from mean sea level, which is computed from continuous observations over a long period, but it gives a quick midpoint for a single cycle.
Why do tidal ranges change through the month?
When the Sun and Moon align, near new and full moon, their gravitational pulls combine to give the largest ranges, called spring tides. Near the quarter moons their pulls partly cancel, giving the smallest ranges, called neap tides. So the range at a place swings between a spring maximum and a neap minimum twice a month.
What datum should the heights use?
Both heights must be measured against the same vertical reference, usually the chart datum, which is typically set near the lowest astronomical tide. As long as both the high and low water heights share that datum, the difference between them gives the correct range regardless of which datum it is.
What units does this use?
The example uses meters, but the calculator works with whatever consistent unit you enter, so feet in gives a range in feet. The arithmetic is a simple difference and average and is deterministic, so the worked example reconciles exactly to the calculator output.
Official sources
- Tides, water levels and coastal observation data: US National Oceanic and Atmospheric Administration (NOAA). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.