Wave energy is one of the most energy-dense renewable resources available at the coast, but it's also one of the least standardized in engineering practice. This guide covers the deep-water wave power formula this calculator uses, what significant wave height and period actually mean, and where the simplified approximation breaks down.
Where the P ≈ 0.5·H²·T formula comes from
The full linear wave theory expression for deep-water wave power density is P = (ρg²/64π)·H²·T, where ρ is seawater density (about 1,025 kg/m³) and g is gravitational acceleration (9.81 m/s²). Plugging in those constants and converting to kilowatts gives the commonly cited coefficient of roughly 0.5, so P ≈ 0.5·H²·T with H in meters and T in seconds yields power in kW per meter of wave front. This is the same approximation used across marine energy resource assessments and academic wave-energy references — it's a first-order estimate of available energy, not a device performance guarantee.
Why height matters more than period
Because the formula squares wave height but only multiplies wave period linearly, height is by far the dominant driver of wave power. Doubling wave height quadruples power density; doubling period only doubles it. A short, steep sea (say 2 m at 6 s) can carry more energy than a longer, gentler swell (1.2 m at 12 s) even though the swell 'feels' more powerful when observed — 2² × 6 = 24 versus 1.2² × 12 = 17.3. This is why coastal wave-energy site assessments weight wave height data heavily and treat period as a secondary, though still important, factor.
From wave power density to device output
Wave power density (kW/m) describes energy flowing past a line in the water — it isn't the output of any particular device. A wave energy converter (WEC) only intercepts power along its physical capture width, and only converts a fraction of that intercepted power to usable electricity, called capture efficiency. Early-stage prototypes often run 10–20% capture efficiency; optimized commercial-scale devices can reach 30% or higher in favorable conditions. Multiplying wave power density by device width and capture efficiency, then by 8,760 hours per year, gives a rough annual energy estimate — useful for early-stage sizing, not a substitute for a hydrodynamic model of the specific device.
Limits of the deep-water approximation
This formula assumes deep water — depth greater than roughly half the wavelength — where the seabed doesn't interact with wave motion. As waves approach shore and enter shallower water, shoaling concentrates their energy into a smaller depth, refraction bends wave direction around headlands and bathymetry, and eventually breaking dissipates energy entirely. None of that is captured by P ≈ 0.5·H²·T. The formula also doesn't model directional spreading (real seas contain waves from a spread of directions, not one clean sinusoid) or extreme-event survival loads. Use this calculator for first-pass resource estimation, and pair it with site-specific bathymetry data and a proper wave model before any serious engineering or investment decision.