Simplified swell power indicator in Gonna.surf

How to interpret swell power

Low power means that the waves are gentle, whereas high power means fast waves, currents, washing machine, getting caught inside.

Here are some pointers:

• 0/5: Very low power. Safe for surfing, probably better with a longer board.
• 1/5: Low power waves.
• 2/5: Gentle waves. Probably the sweet spot for most surfers.
• 3/5: Serious waves.
• 4/5: Very powerful waves. Take safety precautions. Some spots might work well for advanced surfers. Intermediates might want to try surfing in another coast or in a sheltered spot.
• 5/5: Extremely high power. Be very careful, only go surfing to sheltered spots if you know what you are doing.

In addition to the power rating, matching blue bars at the bottom of wave icons visually indicate the power. The darker the blue, the stronger the power is:

Why swell power matters

Have you ever surfed 1.4m waves you felt comfortable with one day, only to struggle the next, despite the same wave height? The difference lies in the swell’s power. Waves from nearby winds (short-period swells) are weaker and slower. In contrast, long-period swells, formed far away, carry more energy and move faster—even at similar heights.

Swell period indicates how established a swell is, but interpreting height and period together can be tricky. Swell power simplifies this by combining both into a single measure of wave energy. It helps forecast conditions more accurately, aiding in safety decisions and board selection.

Get familiar to the values by checking how the power was after your sessions.

How to show swell power in kiloWatts instead of simplified scale.

For people who surf regularly, it is recommended to switch to the power calculated in kiloWatts. as the measure is then more precise than the default power rating going from 0/5 to 5/5.

In the Preferences menu, switch the option "Swell power" to "kW" instead of "Simple", then you are good to go. The preferences are stored in your browser automatically.

Next steps

We keep working on gonna.surf, with plans to write more articles about weather conditions good for surfing, and explaining weather phenomena.

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