The blue litmus will turn red or pink when it comes into contact with an acidic solution below pH 4.5. Between 4.5 and 8.3 the paper will be purple. Above 8.3 it will stay blue. About 100 paper strips supplied in plastic vial.
Litmus paper is NOT used to determine the pH level of a solution. If you need to find out the pH level, the correct test paper to use is the pH paper.