The tide coefficient, explained

What “coefficient 95” means on a French tide table, why it changes every day, and why Brest sets the number.

What is a tide coefficient?

A number from 20 to 120 that tells the size of a tide: the range between a high tide and the following low tide, compared with an average tide. The bigger it is, the higher the sea rises and the lower it falls. At coefficient 100 the range is roughly twice that of coefficient 50.

Spring tides and neap tides

The coefficient follows the Moon: from a maximum (spring tides, just after new and full moon) to a minimum (neap tides, at the quarters) in about seven days, a full cycle in a little under fifteen. Landmarks: 45, average neaps; 70, average tide; 95, average springs; above 100, very big tides.

The biggest tides of the year

They come near the equinoxes (March and September), when the Moon, the Sun and the Earth line up above the equator. Over October 2026 to October 2027, Tide It computes coefficients from 23 to 112.

Why Brest?

The coefficient is computed at Brest, the reference harbour, and applies to the whole coast of mainland France: coefficient 100 is a big tide in Arcachon as in Saint-Malo. What changes from one harbour to the next are the times and heights, not the coefficient.

And for kiting, surfing, shore fishing?

A big coefficient uncovers more sand at low tide (bigger kite beaches, shellfish gathering) but also brings stronger currents and a sea that comes back fast. On tide-dependent spots — a bay, an estuary, a reef — it often decides the session.

French spring tides 2026-2027 calendar →