You should look at the appropriate guide for your type of business premises and judge the appropriate type of extinguisher based upon the risks. In general though you should provide one fire extinguisher for every 200m2, with at least two extinguishers on each floor.
If you operate within a very small premises, and only occupy one floor, then one extinguisher appropriate to the level of risk may be ok. Guidance should be sought from a competent fire extinguisher provider.
