Tap a dot for its tide table. Colour is the water level now, ▲ rising, ▼ falling
tide-table [tides|plan|ports|more] portFive steps from a coast on the map to knowing when the water is where you want it.
Every dot is a port. Amber is low water, blue is high water, ▲ is rising and ▼ is falling, at the moment on the slider. Press play and the tide runs round the coast.
Tap a dot, type a port or a country, or press nearest port. The bookmark saves a port; your saved ports and the last few you opened wait in Ports.
Use the arrows, Today or the date box to jump to any date. In Plan, tap a day of the week ahead to open it.
Times are local time at the port, heights are above chart datum, in metres or feet. Drag across the chart to read the level at any moment: the whole map moves with you.
A spring tide or a coefficient above 90 means a big range and a very low low water. The low tide planner lists the lowest daylight low waters; save them as a calendar file or csv.
The day's range compared with the port's average spring range.
In the six hours from low to high water the tide rises about:
On the map, at the moment on the slider:
A prediction is Moon and Sun only.
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, and puts them on one map so you can see the tide as a movement along a coast and not only as a list of times.
Every port is a dot: amber at low water, blue at high water, ▲ rising and ▼ falling at the moment you choose.
Times and heights for any date, in local time at the port, in metres or feet.
A curve with the sun along the top. Drag across it to read the level at any minute.
Whether today's range is big or small for this port, and the coefficient from 20 to 120.
The lowest daylight low waters of the next weeks, ready for your calendar.
The whole prediction runs in your browser: no server to ask, nothing uploaded. Once the page has loaded, the tables keep working without a connection; only the map tiles need one.
The map answers a question a table cannot: where is the water high right now? Each of the 500 dots takes its colour from the water level at the moment on the slider, compared with the biggest swing that port can make, from amber at low water through pale grey at half tide to blue at high water. The shape of the dot shows the direction: a triangle pointing up for a rising tide and one pointing down for a falling tide. Press play and a day passes in a few seconds. Along the coast of Europe you can watch high water travel up the English Channel and into the North Sea, and on the coasts of Asia you can see the daily tide, which has one high and one low a day, behave differently from the twice-daily tide next to it. The slider covers the day you are looking at and the one after it, in the local time of the port you have open (or your own clock when no port is open). Switch on Size by tidal range in More and the dots grow where the tide is big: the Bristol Channel, the Bay of Fundy and the coast of Normandy stand out at once.
The map is also a way in. Tap a dot to open its table; tap the sea or a beach and the page opens the nearest port within 150 km and tells you how far it is. The list in Ports sorts all 500 by distance, by size of tide or by name, with the level and direction of each at the chosen moment.
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 in the More tab.
Everything is built into the page. Choosing a port or a date does not call any tide service: the prediction is calculated on your device, so it keeps working with the network off once the page is open (only the map tiles need the network). For the map, the page asks the prediction code once per wave for the part that is the same at every port and then adds up each port's own amplitudes and phases, which gives the same numbers as asking port by port, in a few milliseconds instead of a tenth of a second. 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.
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 in More (or press U); heights are rounded to 0.1, feet are metres × 3.28084, and your choice is remembered. The colours on the map are relative to each port's own swing, so a port with a 20 cm tide and one with a 10 m tide both run from amber to blue; the size option shows the difference.
All times in the panel 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 (23 or 25 hours when the clocks change), 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 time slider uses the clock of the open port, with the offset from UTC written under the time. The Copy link button makes an address with the port and the date (?s=…&d=YYYY-MM-DD) and the map view (#v=lat,lon,zoom), so the person you send it to sees the same table.
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 or 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.
French and Belgian tide tables print a number between 20 and 120 next to each tide: the coefficient de marée. It puts the spring and 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.
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; the white line with a dot is the moment on the time slider.
Move the mouse along the chart and it reads out the level at that exact minute; press and drag, or drag a finger, and the time slider and the whole map follow. 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. The table of the day above it lists each high and low water with a bar that shows where its height sits in the day's range; tap a row to put the map at that moment.
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.
In Plan, the week ahead lists high and low water, the coefficient and the spring or neap label for seven days; tap 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. Tap a row to jump to that moment on the chart and the map.
30 days (csv) downloads 30 days of high and low water from the selected day (date, local time, high or low, height, coefficient, spring or neap), with the port, time zone and datum in the first line. All ports now (csv) in More saves the level and direction of all 500 ports at the moment on the slider. Week to calendar adds the week's high and low waters to your calendar as an .ics file, and Planner to calendar does the same for the planner's low waters. All files are created in your browser.
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. A port is also a point: a beach, a harbour or a river mouth some distance away has its own timing, often minutes to an hour different from the nearest port in the list.
The tide prediction runs entirely in your browser. Nearest port 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. The page, the map library and the styles come from this site, the font from Google Fonts, the map tiles from Esri, and the page statistics from SimpleAnalytics, which uses no cookies. Esri sees the tiles you look at, as any map does. In your browser the page stores your saved ports under tide-favs, your last six ports under tide-recent, the unit under tide-unit, the planner settings under tide-planner, your map choices under tide-ui and the light or dark choice under jb-theme. Clear saved data in More removes them.
Check the waves, the sun or the rain before you go. There are more tools in the full list.