Surfer’s guide to Understanding Tides
Introduction
Two Tides a Day
Tides generally follow a cycle of about 12.4 to 12.5 hours, which means we typically experience roughly two high tides and two low tides each lunar day. Over the course of a week, this results in 13-14 high tides and 13-14 low tides, creating a predictable rhythm for surfers and coastal dwellers alike.
This cycle is driven primarily by the Moon’s gravitational pull on the Earth’s oceans, with the Sun’s pull modulating the intensity. The Moon actually raises two bulges of water at once — one on the side of the Earth facing the Moon, where its pull is strongest, and one on the opposite side, where the water is effectively left behind as the Moon draws the planet itself away from it. As the Earth spins through these two bulges, most coastlines pass through two high tides and two low tides. Here in Bali the pattern is a mixed one, where the two daily high tides are often slightly different heights.
The slight difference from a perfect 12-hour cycle means the timing of tides gradually shifts each day, repeating roughly every 24 hours and 50 minutes. This is why low tide and high tide come a little bit later every day. The reason is that the Moon is also orbiting the Earth — over about 29.5 days, in the same direction the Earth turns — so each day the Earth has to rotate a little further to bring the same point back beneath the Moon, which takes that extra 50 minutes. In practice this matters: a tide that is perfect for a reef break at 7am today will be right at roughly 7:50am tomorrow, so always check a local tide table rather than relying on memory.
The Moon and the Sun: What Really Drives the Tides
It is not only the Moon. The Moon accounts for roughly 70% of the tide-generating force and the Sun the remaining 30% — the Sun’s pull is about half the Moon’s. That surprises most people, because the Sun is around 27 million times more massive than the Moon and you would expect it to dominate. The reason it does not is distance. What matters for tides is not the raw strength of gravity but the difference in pull between the near and far sides of the Earth, and that difference falls away very steeply with distance — with the cube of it. The Sun is about 390 times further away than the Moon, and that distance almost entirely cancels out its enormous mass advantage. As our Science of Waves guide explains, this is why the much closer Moon, not the Sun, sets the rhythm of the tides.
Understanding this cycle helps surfers anticipate the best times to catch waves, as different stages of the tide can greatly affect wave size and shape. Watching for those larger spring tides or the calmer neap tides can make all the difference in planning your perfect surf session!
You need detailed knowledge of the surf spot to pick the best tide and use this in conjunction with the swell size, to pick the best spot. Dreamland A frame, Padang Padang Lefts and Outside Corners are all best on a dead low tide but will stop breaking at mid-tide and above unless the swell is exceptionally big. The Racetrack is a low tide break but a spring low tide is too low. Coincidentally Bingin works best on same tide as the Racetrack but Balangan needs a higher tide to work well. Green Bowl will work on any tide but the left only works at dead low. Both Pandawa and Nyang Nyang are best at high tide. All the Nusa Dua breaks suffer from a very strong current at high tide, except for Mushroom rock as it is protected by a headland.
Spring Tides and Neap Tides: The Big and Small Swells
There are two special types of tides that surfers need to get familiar with—spring tides and neap tides.
- Spring Tides: These happen during a full or new moon when the sun, moon, and Earth are aligned. Their combined gravity pulls more strongly on the oceans, causing especially high high tides and low low tides. The waves can get bigger and more powerful, perfect for a serious surf session.
- Neap Tides: During the moon’s first and third quarter phases, the sun and moon are at right angles relative to Earth. Their gravitational forces partially cancel each other out, leading to smaller differences between high and low tide. Expect gentler, less intense waves that are great for beginners or when you want a more mellow surf.
The difference between the two is significant: the tidal range on a spring tide is typically 20–40% larger than on a neap. The full lunar cycle takes about 29.5 days and gives two spring periods (new moon and full moon) and two neap periods (the quarter moons), each lasting roughly a week — so the tide swings between maximum and minimum range on a 14-day rhythm.
Why It Matters to Surfers
Understanding how the sun and moon work together can help you plan your surf sessions. During spring tides, the bigger waves often mean more exciting rides, but be mindful of currents. Neap tides can be calmer and more predictable, perfect when you are working on your skills or seeking smaller, more manageable waves.
So next time you are eyeing the beach, check the tidal cycle—knowing when the tides are at their peak or trough can be the difference between a good surf and a great one!
Which tide is best?
It absolutely depends on the individual surf spot characteristics and how this interacts with the swell size, wave period and swell direction. It is how the ocean’s floor—the bathymetry—interacts with tides and waves that determine the quality for surfing. For example if too fast and closing out, then not surfable. Bathymetry refers to the underwater topography, such as reefs, sandbars, and seabed slopes, which strongly influences wave formation.
When tides rise and fall, they change the water depth over these underwater features. During low tide, shallow areas like sandbars and reefs are exposed, causing waves to slow down, rise up, or even break more suddenly and dramatically. At high tide, deeper water can let waves travel farther and break farther offshore, resulting in more manageable, peeling waves.
Certain bathymetric features, like reefs or points, serve as natural wave shapers. During specific tide phases, these features can focus wave energy, creating powerful, well-formed surf. Conversely, during other tide levels, waves may become choppy or less defined.
In essence, tide levels and underwater terrain work together to influence wave size, shape, and timing. Knowledge of the local bathymetry combined with tide forecasts can help surfers choose the best time to ride specific breaks, ensuring a better session with cleaner, more rideable waves.
In general reef breaks are best at mid tide. At high tide there can be too much water on the reef and the waves will stop breaking if too deep, or could be too fat to ride. Conversely at low tide the waves can form up outside of the reef and then dump onto the reef. If the surf spot is best at mid-tide then neap tides are much better for surfing as the tide can be good all day or most of the day. If spring tides, the tide moves in and out much faster which means stays at low tide for a much shorter time.
To help understand the characteristics of each surf spot in Bali, we have written a comprehensive guide on what spots work under the best conditions and what tides are optimal.
We have also written a guide on reading a swell forecast which is essential, in conjunction with a tide chart, and knowledge about the surf spot, to determine the optimal tide and location to surf. Nothing is easy about surfing and the more effort and research you put into it, the more you will get out.
You can easily get benchmark indicators for surf spots such as best at high tide or mid tide, but it is far more nuanced than that, as the tide needs to be considered with technical factors such as wave period, and there can be huge difference between neap and spring tides. If you are unfamiliar with a surf spot we recommend for beginner and intermediate surfers start out for at least the first few days with a reputable local surfing operator who will know how the tides interact with other factors.