The difference in water level between successive high and low tides is the tidal range. It varies from place to place and from day to day. Microtidal coasts experience ranges smaller than two meters; macrotidal coasts can see ranges exceeding six meters, and a few locations exceed fifteen meters.

Range is controlled by the astronomical tide-generating forces, the resonance properties of the coastal basin, and the local bathymetry. Spring tides produce the largest ranges; neap tides the smallest. Funnel-shaped bays and broad continental shelves can amplify the tidal wave dramatically.

Tidal range determines the extent of the intertidal zone, the design of ports and coastal defenses, and the potential for tidal energy extraction. Organisms living between the tide marks are adapted to the local range and the associated cycles of emersion and submersion. Accurate prediction of tidal range is one of the oldest and most successful branches of geophysical forecasting.

• Height difference between high and low tide
• Varies geographically and with the spring-neap cycle
• Amplified by coastal geometry
• Shapes intertidal ecosystems and coastal engineering