Important notes
- 2 days with identical surf height can have different energy depending on the underlying swells
- Other factors (e.g. the depth of the water and gradient of the beach, the tide, and the sandbars/reef) will affect how powerful the surf feels
- 300kJ could be really powerful at one beach but less so at another, due to how the waves approach that spot and the effect of differences in the ocean floor.
- For anyone making home-calculations, be sure to use metric units!
Why use this new metric?
It is useful to have a single unit that brings together height and period.
Wave size is still a good indicator to know your limits. However, as the largest contributor to energy is wave height, you might want to start taking note of energy, too.
If 4-5ft is your limit because you've had good days and bad days at that size, the energy might tell you the crucial difference!
Get a headstart on understanding this metric - energy is showing on our historical forecasts! Find some memorable days (for better or for worse) and create a mental record of your threshold.
How is it calculated?
Wave Energy is a function of swell height and period, measured in kilojoules (kJ), a standard unit of energy. Wave energy is also calculated based on the relative direction of the swell to the beach. The overall energy value is calculated as the sum of the energy of the individual partitions and those are calculated taking into account the impact on a given spot.
Power is the swell height squared multiplied by period (and some coefficients), which means height has proportionally more effect on power than period does
Thought period was the key to swell power? 2ft at 20 seconds may be more effective at creating the type of waves you want to ride - but by definition has less power.
Power or energy? The wave power is just the rate at which the energy from the waves is transported
Where can I find it?
A dedicated column on the alternative forecast layout! Forecast layout toggle
Wave Energy graph under the Labs section of spot pages. This shows the combined power of all swells.
Order by power on the swell graph to change the Y axis from ft to kJ.
Individual swell partitions. Hover your mouse over any individually sorted swell to see the energy value. Looking at individual swells helps you understand the relationship between energy, height & period. The height and period of a wave determine the energy it carries.
Surfline's charts. There is a new Wave Energy layer!
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