Plus petit vs. moindre
While both plus petit and moindre translate to meaning smaller or lesser, they belong to different registers and contexts. Generally, plus petit is used for concrete, physical comparisons, whereas moindre is reserved for abstract concepts and formal expressions.
Plus petit
A1This is the standard comparative form of petit. It is used to describe physical size, height, age, and concrete measurements. If you can measure it with a ruler or seeing it with your eyes, you should generally use plus petit.
Mon nouvel appartement est plus petit que l'ancien.
(My new apartment is smaller than the old one.)
Il est plus petit que son frère de trois centimètres.
(He is smaller than his brother by three centimeters.)
Tu devrais prendre un morceau plus petit.
(You should take a smaller piece.)
Ce téléphone est plus petit mais plus puissant.
(This phone is smaller but more powerful.)
Moindre
B2This word is used for abstract comparisons involving value, importance, degree, or intensity. It is more formal than plus petit and often translates to lesser, lower, or slightest. It is rarely used for physical size.
Nous devons choisir le moindre mal.
(We must choose the lesser evil.)
Je n'ai pas la moindre idée de ce qu'il fait.
(I do not have the slightest idea of what he is doing.)
Le risque est moindre si vous conduisez prudemment.
(The risk is lower if you drive carefully.)
Ils ont acheté ce produit à moindre coût.
(They bought this product at a lower cost.)
Summary
To choose correctly, ask yourself if the smallness is physical or abstract. Use plus petit for physical dimensions like height and area. Use moindre for abstract concepts like impact, chance, cost, or importance, especially when you mean lesser or slightest.