Learn Finnish: Polku oli sen verran huono, että uudet kengät alkoivat hiertää. - The path was so bad that the new shoes started to chafe.

While niin huono, että simply means 'so bad that', sen verran stresses the exact extent or degree of the badness. You can think of it as meaning 'bad to the extent that' or 'just bad enough that'.

What exactly is the word verran in this construction?

It is the genitive form of the noun verta, which means an amount or quantity. Combined with the genitive pronoun sen (that), sen verran literally means 'the amount of that' or 'that much'.

Why is the verb hiertää in the basic dictionary form rather than hiertämään?

The verb alkaa traditionally requires the basic first infinitive, so alkoivat hiertää is the standard written form. While alkoivat hiertämään is very common in modern spoken Finnish and is now officially accepted, the first infinitive remains the safest choice for formal writing.

Is hiertää the standard verb for shoes giving you blisters?

Yes! Hiertää means to chafe, rub, or cause friction. When talking about shoes or clothing rubbing uncomfortably against your skin, it is the most natural verb to use. You might also hear the verb hankaa used in the exact same way.