Grande vs. largo
In Spanish, grande and largo are both used to describe size, but they are not interchangeable. The key difference is that grande refers to overall size (big), while largo refers specifically to length (long).
Grande
A1This word means big or large. It describes the general, overall size of an object, considering its height, width, and volume. It is the opposite of pequeño (small).
Compramos una mesa grande para el comedor.
(We bought a large table for the dining room.)
México es un país muy grande.
(Mexico is a very big country.)
Ese perro es grande pero muy amigable.
(That dog is big but very friendly.)
Tenemos un problema grande que necesita solución.
(We have a big problem that needs a solution.)
Mi abuela me dio un abrazo grande.
(My grandmother gave me a big hug.)
Quiero una porción grande de papas fritas.
(I want a large portion of french fries.)
Largo
A2This word means long. It describes only one dimension: length. It is used for things like distance, duration, or objects that are longer than they are wide. It is the opposite of corto (short).
El río Nilo es el río más largo de África.
(The Nile River is the longest river in Africa.)
Ella tiene el pelo largo y oscuro.
(She has long, dark hair.)
El viaje en tren fue muy largo.
(The train journey was very long.)
Necesito un pantalón más largo.
(I need a longer pair of pants.)
La película me pareció demasiado larga.
(I found the movie to be too long.)
La lista de tareas para hoy es muy larga.
(The to-do list for today is very long.)
Summary
In short, use grande when you mean big or large in a general sense (like a big house or a large pizza). Use largo when you specifically mean long in one dimension (like long hair, a long road, or a long movie). A snake can be larga (long) but not necessarily grande (big/thick), while an elephant is always grande (big).