[Groff] How to change the width for groff ascii output

[Procházka Lukáš Ing . - Pontex s . r . o .]

Hello,

I have a text file which is reformatted by groff to another ascii file. But 
width of the output page is 66 characters and I'd rather have 80 characters.

How do I change it?

WinXP user, I use "groff.exe -Tascii source.txt > result.txt" to reformat file.

Thank you in advance.

Lukas