Using spaces and different punctuation marks in Finnish is not easy. I think most Finns do not even know all the rules; I did not learn all the details at school, although I was good in writing. Often I have to check a rule in a handbook of orthography.
When writing e.g. “ks. sivut 16–21” (“see pp. 16–21”), in Finnish one should use the en-dash without spaces. The em-dash is not recommended in Finnish.
However, if the en-dash cannot be used, then one can use the hyphen with spaces on both sides: “ks. sivut 16 – 21“.
And it seems WordPress cannot make a difference in length between the hyphen and the en-dash…!
A hyphen is the shortest, an en-dash is the width of the letter n and an em-dash is the width of the letter m.
The hyphen can be created by Alt +45 on the numerical keyboard; the codes for en-dash and em-dash are Alt +0150 and Alt + 0151, respectively.
A good handbook for finding all the rules is Kielitoimiston oikeinkirjoitusopas.