A line should typically be a maximum length of 80 characters.

[Pink_Flower]

A line should typically be a maximum length of 80 characters.
A line should typically have a maximum length of 80 characters.
Source: myself

Which one is more accurate and better?

 

[emsr2d2]

They're both possible. I'd reword and shorten it though.

A line should contain a maximum of 80 characters.
A line should consist of no more than 80 characters.

 

[jutfrank]

I really don't like the first one. be a length? Yuck. I say it's wrong.

The second one is much better, but the suggestions in post #2 are how you should say it.

 

[Charlie Bernstein]

And since you're writing it for yourself, you might like knowing that while digital code writers like eighty characters per line, typographers recommend fewer for ordinary reading. For example:

40 to 75 characters
45 to 75 characters
50 to 60 characters
70 characters