What’s the difference between “unos”/“unas”, “sobre”, and “tantos” for approximations?

Question

Hola Kwiziq Team,

What’s the difference between “unos”/“unas”, “sobre”, and “tantos” for approximations for numbers. The words “unos”/“unas” and “sobre” can mean “about” before a number. Examples: Debería terminar mi trabajo en unos dos minutos. / Debería terminar en sobre dos minutos. I’m wondering if “unos”/“unas” are more common and less formal than sobre. Can the word “tantos” mean “around” used in a similar way to “unos”/“unas” and “sobre”? Example: Creo que este objeto tiene tres mil y tantos años de antigüedad.

Silvia Piriz · Accepted Answer

Hola Kieran B.
That’s a really good and thoughtful question!
You’re right that “unos / unas” are the most common way to express approximation in Spanish. We use them all the time in everyday speech, for example:
Llegará en unos cinco minutos. (“He’ll arrive in about five minutes.”)
It’s the most natural and neutral option.
“Sobre” can also mean “about” or “around”, but it sounds a bit more formal or written. You’ll see it used in sentences like Costará sobre cien euros (“It will cost about a hundred euros”), but it’s less frequent in spoken Spanish.
As for “tantos / tantas”, it doesn’t mean “around”. It’s used instead to express “so many” or “that many”.
For example:
Tiene tantos años como su hermano. (“He’s as old as his brother.”)
 or
Hace ya tantos años de eso... (“That was so many years ago…”).
In your example, tres mil y tantos años means “three thousand and something years”, not “around three thousand years.”
I hope this helps clear things up! It’s a subtle distinction, but a great one to notice.
Best, Silvia