If the HCl is 32%, you would put 18.75 ml of 32% HCl in to a measuring device and add enough water to make 100 ml. The last bottle I picked up was 31.45%, and that required 19 ml in a measuring device and enough water added to make a total of 100 ml. As you can see, the dilution depends upon the initial strength of the acid.
To do a room, you can start with 10 ml. If that seems off, you can adjust up or down from there.