This model lets you compare shapes. Its wave heights have no real-world units. It does not calculate wind conditions or predict the sea.
Wind transfers energy to water
Wind blowing over the sea transfers energy to the water, generating waves. Waves growing under the local wind are called wind waves. Out at sea, waves of different shapes and sizes overlap.
Our diagram shows one regular wave so that differences are easier to see. Move the slider and watch the vertical distance between a crest and a trough change.
Height, length and time
Wave height is the vertical distance from trough to crest. Wavelength is the distance from one crest to the next. Wave period is the time between successive crests passing a fixed point.
A high wave and a wave with widely spaced crests describe different things. This model changes wave height while keeping wavelength the same.
Swell can arrive from far away
Waves that travel beyond the wind that generated them, or remain after that wind has weakened, are called swell. Waves from a distant typhoon can reach a coast far from the storm.
Swell can grow higher as it approaches shallow coastal water. Sunny weather and light local winds alone do not tell you the shore is safe. Check the latest weather and sea information before your visit.
LET’S THINK
A question to explore
When you make the wave bigger in the diagram, which changes: wave height or wavelength?
Show a hint and explanation
Wave height changes; wavelength stays the same. Compare the distance between successive crests to check. In the real sea, several characteristics can change at once.
Explore together, at home or in class
Draw a side view of a wave. Explain the difference between height, distance and time. A still picture can show height and wavelength; measuring period needs an observation over time.
Sources & further reading
We developed our own explanations and diagrams using these sources. Inclusion does not imply review, endorsement or affiliation by the source organisation. Links marked “Japanese” lead to Japanese-language material.
- [1] Japan Meteorological Agency: understanding waves (Japanese) ↗Wave height, wavelength, period, wind waves, swell and changes in shallow water.
First published: 2026-09-20 · Updated: 2026-09-20 · Sources checked: 2026-09-20 · Editorial policy