Approximate numbers can be expressed using a numeral preceded by the adverb noin, suunnilleen, osapuilleen, likimain, likimäärin or (colloquially) about ∼ öbaut, e.g. noin viisi (about five). There is no big difference between these adverbs, but the shortest one, noin, is the most common, and in contrast, the other adverbs tend to be emphasize the approximateness to some extent.
Alternatively, expressions like viiden tienoilla or (colloquially) viiden hujakoilla can be used; tienoo means area or region, so literally viiden tienoilla means “in the region of/around five”.
As in English, the mathematical symbol “≈” or, as its replacement, the tilde “∼” is sometimes used instead, but notations like ≈ 5 are informal style, except in mathematical formulas.
For numbers 3–10, words derived from cardinal numerals with the isen suffix can be used to indicate an approximate number, e.g. kolmisen = noin kolme (about three). They have some irregular variation in the stems: kolmisen, nelisen, viitisen, kuutisen, seitsemisen, kahdeksisen, yhdeksisen, kymmenisen.
For tens, thousands, millions, etc., such words can be used as the first part of a composite numeral, e.g. viitisenkymmentä = noin viisikymmentä (about fifty). Similarly, we have the approximate numerals from kolmisentoista (about thirteen) to yhdeksisentoista (about nineteen).
For one hundred and one thousand, the words satakunta and tuhatkunta can be used.
All these approximate numerals can be used only in association with a noun, not as standalone. They are used like normal cardinal numerals so that the associated noun is in partitive singular, e.g. kolmisensataa euroa = noin kolmesataa euroa (about three hundred euros). However, if the expression as a whole needs to be in a case form other than the nominative, these words cannot be used; we can only say e.g. noin kolmellasadalla eurolla.
For the number 2, we can use the indefinite pronoun pari, e.g. pari euroa, though it has a rather vague meaning. It may mean “two or three”, or “about two” (e.g. 1.80 euros would probably be counted as pari euroa), or a more vague small amount.
Finnish uses phrases like Hän on kolmissakymmenissä (He/she is about thirty years old), with a word for tens, kolmekymmentä, in inessive plural. However, a simpler analytic expression like Hän on noin kolmekymmentä is probably more common.
This should not be confused with expression like Hän on neljännelläkymmenellä (He/she is in his/her thirties), which means that the person’s age is 30–39 years.
To express “a little over…”, we can say vähän yli… or hiukan yli… or, in literary style, jonkin verran enemmän kuin… In informal language, we can also say reilut…, but in inflected forms, this word turns to singular, e.g reilut sata euroa : reilulla sadalla eurolla.
Similarly, “a little under…” can be expressed with vähän alle…, hiukan alle…, hiukan vähemmän kuin…, or vajaat… Example: vajaat viisi metriä : vajaata viittä metriä.