Spanish c vs z pronunciation: the k, s and th sounds

The letter c has two sounds in Spanish, decided by the vowel after it. Before a, o or u it is a hard k (casa, cosa, cuna). Before e or i it becomes a soft sound (cena, cine). The letter z always has that same soft sound.

Here is the part that surprises learners: what the soft sound is depends on where the Spanish is spoken. In most of Spain it is the English “th” in think; in Latin America and southern Spain it is a plain “s”. Both are fully correct standard Spanish — this is seseo (using s) versus distinción (using th), not right versus wrong.

Hard c: the k sound

Before a, o or u, and before a consonant, c is a hard k, the same as in English car.

casa, como, cuna
house, I eat, cradle

This sound never changes by region — a hard c is a k everywhere.

Soft c and z: th or s

Before e or i, the c softens, and z carries that soft sound in front of any vowel. Whether you say “th” or “s” is simply your accent.

cena, cielo, zapato, zumo
dinner, sky, shoe, juice

A speaker from Madrid says cena like “THE-na”; a speaker from Mexico City or Buenos Aires says “SEH-na”. As a learner you can pick either and be understood everywhere; most learners aiming at Latin American Spanish use the “s”, while those aiming at Spain use the “th”.

Why the k sound is spelled two ways

Because a soft c exists before e and i, Spanish needs another letter for a hard k in front of those vowels — that letter is qu. So the k sound is c before a/o/u and qu before e/i.

casa, cosa, cuna — but queso, quince
house, thing, cradle — but cheese, fifteen

The same logic runs backwards with z: Spanish avoids z before e/i and writes c instead. That is why the plural of lápiz is lápices, and why empezar becomes empecé in the past.

This swap shows up all the time once you notice it: cinco and once use c for the soft sound before e/i, while zumo and azul use z before a/o/u. The sound is identical; only the spelling follows the vowel.

A quick regional guide

You do not have to pick an accent to be understood, but it helps to know the map. All of Latin America uses seseo, pronouncing soft c and z as a plain “s”. Most of central and northern Spain uses distinción, keeping the “th” sound distinct from “s”. A third pattern, ceceo (pronouncing even the letter s as “th”), exists in parts of southern Spain and is more local.

gracias, cerveza, centro
thank you, beer, city center

For a learner, the practical takeaway is simple: choose “s” everywhere if you are aiming at Latin American Spanish, or “th” for soft c and z if you are aiming at Spain. Either choice is consistent and correct.

Common mistakes

Pronouncing z like the English z

Spanish z is never the buzzing English z of zoo. It is “th” or “s”, but never a voiced z.

zapato with a buzzing z → “thapato” (Spain) or “sapato” (Latin America).
The z has no voiced buzz in Spanish.

Reading ce/ci as a k

Before e or i, the c is soft, not hard.

cena said as “KEH-na” → “THE-na” or “SEH-na”.
A c before e or i is never a k.

Forgetting the z-to-c spelling swap

Before e or i the sound is written c, not z.

lápizes, empezé → lápices, empecé.
Pencils; I started.

Sounds like this one are easiest to fix by ear, hearing the same word in both accents and copying whichever you are aiming for. In Fluera every word plays with native audio, so you can hear cena and zapato and match the accent you want — a practical way to practice Spanish next to the other tricky sounds like the rolled rr, the Spanish j and b vs v.

Practice