More usual here is lines of destination text. A line is a DIN line from a typewriter, 55 characters including spaces.
Charge rates to the end customer vary depending on the nature of the text. Typical for average is about €1 to €1,20 per line, so agencies may only want to pay you 50 to 80 Cent per line.
Personally, I charge direct customers €1 per line for simpler technical texts, and as much as possible for the hard stuff

Some will charge around 6 to 8 cent per word but, as said, it's not usual here.
Just be aware that, if the text is of a legally binding nature,
a liability disclaimer is a good idea.
If somebody has a financial disadvantage because of your work, they will often enough try to get compensated for that. That has been the end of many a friendship :excl:
For estimating quotes, look at the number of characters
including spaces in the "Statistics" tab in Word, divide by 55 and add 10%.
Expect to do about 50-60 lines per Hour when you're up and running, maybe 40 to start with. That might even be as low as 10-20, if you are having to use the dictionary a lot. Remember that the overheads: Estimating, organizing and invoicing all take time on top, as do collection, delivery and discussion. For short texts, the overheads can be more than the work itself.
If the customer is happy with paying what comes out in the end, then do the math with the final text. (I generally point out to them that this is usually cheaper for them, but most want a quote up front.)
Of course there is the dreaded USt to add on to that.
You can also consider "special" prices for friends and 007 jobs