Tide Table — high and low water, tide chart and coefficient
High and low water for 500 ports in 85 countries, with heights above chart datum, a chart you can drag to read the water level at any moment, and the two numbers most tide sites leave out: whether today is a spring or a neap, and the tide coefficient. The whole prediction runs in this page — the harmonic constants are built in, so there is no server to ask and nothing to upload.
| Day | High water | Low water | Coef | Tide |
|---|
Guide — reading a tide table
Type a name, or press nearest to me. Press ☆ save to keep a port in your list at the top, and your last few ports are remembered too.
Use the arrows, today or the date box to jump to any date. Click a row in the week ahead to open that day.
Times are local time at the port, heights are above chart datum, in metres or feet. The chart shows day and night along the top.
A spring tide or a coefficient above 90 means a big range: very low low water, strong currents. A neap moves the water much less.
The low tide planner lists the lowest daylight low waters for the coming weeks. Save them as CSV or add them to your calendar with .ics.
The day's range compared with the port's average spring range.
- 20–40
- weak neap: the water barely moves
- 45–70
- ordinary tides
- 70–95
- strong: good low water
- 95–120
- very strong, around the equinoxes
In the six hours from low to high water the tide rises about:
- hour 1
- 1/12 of the range
- hour 2
- 2/12
- hours 3–4
- 3/12 each: half the change
- hour 5
- 2/12
- hour 6
- 1/12
A prediction is Moon and Sun only.
- Wind
- onshore wind and low pressure raise the water, often by tens of centimetres
- Timing
- be back well before low water turns
- Official
- for navigation, use your national hydrographic office
Tide tables, explained
A tide table lists the moments the water stops rising and starts falling, and the other way round: high water and low water, with the height the water reaches. Most coasts get two of each a day, roughly every 12 hours and 25 minutes, which is why high water comes about 50 minutes later each day. Some places, such as parts of the Gulf of Mexico, get only one high and one low a day; others have a mixed tide with two clearly unequal highs. This page predicts all three kinds for 500 ports in 85 countries, from Aasiaat in Greenland to the Antarctic coast.
How the tides are computed
Tides are predicted by harmonic analysis. Years of measured sea level at a port are split into a set of sine waves, the tidal constituents, each with a period fixed by astronomy: M2 for the principal lunar tide (12 h 25 min), S2 for the solar one (12 h), K1 and O1 for the daily tides, and many smaller ones for the Moon's changing distance and the tilt of its orbit. Each port has its own amplitude and phase for every wave. Add the waves back together for any date, past or future, and you have that port's astronomical tide.
All 500 ports use harmonic constants from TICON-4, a global set derived from the GESLA-4 sea-level archive and published under a CC BY 4.0 licence, taken from the openwatersio tide-database project. The 16 US ports come from the same source (University of Hawaii Sea Level Center gauges and state networks such as Louisiana's CRMS), so they are not NOAA's official predictions and can differ slightly from NOAA's own tables. Each port ships with between 6 and 50 constituents (32 on average, from a list of 50); waves smaller than 3 mm are left out to keep the page small. The summation code is adapted from the MIT-licensed @neaps/tide-predictor, and the source and licence of the selected port are shown under its name.
Everything is built into the page. Choosing a port or a date does not call any tide API: the prediction is calculated on your device, so it keeps working with the network off once the page is open. Sunrise and sunset use the NOAA solar position algorithm (the same code as the golden hour calculator), and the moon phase uses a mean-phase approximation that is good to a few hours.
Heights and chart datum
The heights are not depths and not distances from the beach. They are heights above chart datum, a fixed level that nautical charts measure their depths from, chosen so that the sea rarely falls below it. If the chart shows 2.4 m at a spot and the table says 3.1 m, there is about 5.5 m of water there. The datum is named under the port name, in the chart readout and in the CSV header, because countries use different ones:
| Datum | Meaning | Ports here |
|---|---|---|
| LAT | Lowest Astronomical Tide | 365, including the UK, France, the Netherlands, Ireland, Australia and the German North Sea coast |
| MLLW | Mean Lower Low Water | 27: the United States, the Philippines and several Pacific islands |
| MLWS | Mean Low Water Springs | 26: Italy, Brazil and Chile |
| LLWLT | Lower Low Water, Large Tide | 24: Canada |
| NLLW | Nearly Lowest Low Water | 14: Japan |
| TLT | Theoretical Lowest Tide | 7: China |
| MSL | Mean Sea Level | 37 Baltic and Kattegat ports in Sweden, Germany, Denmark and Finland |
With LAT and the other low-water datums nearly every height is positive. The 37 MSL ports are the exception: their tide is only a few centimetres, so heights are given around mean sea level and low water shows as a negative number. Switch between metres and feet with the m / ft buttons; heights are rounded to 0.1, feet are metres × 3.28084, and your choice is remembered.
Times and time zones
All times are local time at the port, including summer time, whatever time zone your own device is set to. A day runs from local midnight to midnight at the port, so a table for Sydney read in Brussels still shows Sydney's day. The 500 ports cover 151 time zones, and the zone is written into the CSV export. The 🔗 link button copies an address with the port and the date (?s=…&d=YYYY-MM-DD), so the person you send it to sees the same table.
Spring and neap tides
The Moon raises the tide; the Sun raises a smaller one, a little under half the size. Twice a lunar month, around new moon and full moon, the two line up and reinforce each other: a spring tide, with the highest highs and the lowest lows of the fortnight. Around the quarter moons they pull at right angles and partly cancel: a neap tide, with a much smaller range. "Spring" has nothing to do with the season; it is the older sense of the word, the tide springing up.
The difference is large. At Dover a spring range is roughly twice a neap range, so the same beach can show hundreds of metres more sand in a spring week. If your plan depends on how far the water goes out (a walk to a tidal island, launching from a slipway, a dive on a wreck) the spring/neap label matters as much as the exact time.
Springs usually arrive a day or two after the new or full moon, and the delay differs from port to port. Instead of assuming it, this page compares each day's range (highest high minus lowest low) with the smallest and largest daily range the port reaches in the 30 days around it. The top 28% of that span is labelled spring, the bottom 28% neap, and the rest mid-range. That keeps the label right on coasts where the moon-phase rule of thumb fails.
The tide coefficient
French and Belgian tide tables print a number between 20 and 120 next to each tide: the coefficient de marée. It puts the spring/neap question into one figure.
| Coefficient | Means | In practice |
|---|---|---|
| 20–40 | weak neap | the water barely moves; poor for anything that needs a big drop |
| 45–70 | average | ordinary conditions |
| 70–95 | strong spring | good low water; strong tidal streams |
| 95–120 | very strong | the biggest tides of the year, usually around the equinoxes |
Officially the coefficient is calculated for Brest and used along the whole French coast. Because it is a ratio rather than a height, the idea carries over to any port. Here it is computed per port as day's range ÷ (MHWS − MLWS) × 100, where MHWS − MLWS is the port's mean spring range (all 500 ports publish both levels), rounded and limited to 20–120. One difference to know: in the French tables an average spring tide is 95 and 100 is an average equinoctial spring, while here an average spring tide is 100, so these numbers run a few points higher than the official French ones. Coefficients above about 110 occur on only a few days a year.
How to read the tide chart
The curve is the water level above chart datum. High and low water are marked with their times and heights. The coloured band along the top follows the real height of the sun at the port (dark night, twilight colours, daylight), and the same colours are washed faintly behind the water, so you can see at a glance whether a low tide falls in daylight. The dashed red line with a dot is now.
Move the mouse or your finger along the chart and it reads out the level at that exact moment, not snapped to a ten-minute grid. That is usually the real question: not "when is high water" but "will there be enough water at half past four". Switch between 1, 3 and 7 days with the buttons under the chart.
To do it in your head, use the rule of twelfths: in the six hours from low to high water, the tide rises 1/12 of its range in the first hour, then 2/12, 3/12, 3/12, 2/12 and 1/12. Half the movement happens in the middle two hours. It assumes a smooth twice-daily tide, so it works well in the English Channel and badly where the tide curve is distorted. Compare it with the curve here to see whether it holds at your port.
The week ahead, the low tide planner and exports
The week ahead lists high and low water, the coefficient and the spring/neap label for seven days; click a row to open that day. The low tide planner searches the next 14, 30 or 60 days for low waters with a coefficient of at least 70, 85 or 95 (or any), optionally only between sunrise and sunset, and marks the three lowest. Click a row to jump to that moment on the chart.
⬇ csv 30 days downloads 30 days of high and low water from the selected day (date, local time, high/low, height, coefficient, spring/neap), with the port, time zone and datum in the first line. 📅 .ics adds the week's high and low waters to your calendar, and add to calendar in the planner does the same for the planner's low waters. Both files are created in your browser.
How accurate is it? Not for navigation
A tide table is an astronomical prediction: Moon and Sun only. It does not know about air pressure, wind, storm surges or river flow. A deep low and an onshore gale can keep the real level half a metre above the prediction for a day, and a storm surge can add several metres. Rivers and estuaries add their own delays. Use this page for planning a walk, a swim or a fishing trip, and use the official tables of your national hydrographic office for navigation and anything else where being wrong matters.
Two smaller limits: a port whose original sea-level record was short or noisy is less well described than one with decades of clean data, and the left-out constituents are each under 3 mm. Neither comes close to the effect of the weather.
Privacy
The tide prediction runs entirely in your browser. 📍 nearest to me asks your browser for your location and uses it only on this page to find the closest of the 500 ports; the coordinates are not sent anywhere. Saved ports, your last six ports and the m/ft choice are kept in your browser's localStorage. The only outside requests are the Google Fonts stylesheet and Simple Analytics, a cookie-free page-view counter.