French flag

Sûr vs. sauf

Word practice demo
While the French words sûr and sauf can appear similar to English speakers, especially since both can relate to the concept of "safe", they have very distinct primary meanings and are generally not interchangeable.

Sûr

A1
The word sûr is an adjective with two main meanings. Firstly, it means sure or certain, expressing a lack of doubt. Secondly, it means safe or secure, referring to protection from danger. As an adjective, it must agree in gender and number with the noun it modifies (sûr, sûre, sûrs, sûres).
Je suis sûr que tu as raison.
(I am sure that you are right.)
Elle est sûre de sa décision.
(She is sure of her decision.)
C'est un endroit sûr pour les enfants.
(It is a safe place for children.)
Assurez-vous que la porte est bien sûre.
(Make sure the door is properly secure.)
Nous sommes sûrs de vouloir continuer.
(We are sure we want to continue.)
Bien sûr, vous pouvez utiliser mon téléphone.
(Of course, you can use my phone.)

Sauf

A2
The word sauf is primarily used as a preposition meaning except or save for. It is used to introduce an exception to a statement. While it can mean safe in the fixed and common expression sain et sauf (safe and sound), this usage is otherwise very rare, formal, or archaic.
Tout le monde a fini, sauf moi.
(Everyone has finished, except me.)
Le musée est ouvert tous les jours, sauf le lundi.
(The museum is open every day, except on Mondays.)
Il mange de tout, sauf des épinards.
(He eats everything, except for spinach.)
Nous sortirons, sauf s'il pleut.
(We will go out, unless it rains.)
Malgré l'accident de voiture, le conducteur était sain et sauf.
(Despite the car accident, the driver was safe and sound.)
La lettre est parfaite, sauf pour une ou deux fautes de frappe.
(The letter is perfect, save for one or two typos.)

Summary

In summary, the key difference is function and common usage. Use sûr as an adjective for sure (certainty) or safe (security). Use sauf almost exclusively as a preposition for except. The only common context where sauf means safe is within the specific phrase sain et sauf.