Since I am a chemist, I can speak from experience. A dilution written as 1:3 has always been 1 part of A mixed with 3 parts of B. What may change from time to time is the units of measurement. For example 1:3 may be followed with v:v which specifies the unit of measurement is volume of each part or 1:3 may be followed with wt:wt which specifies the unit of measurement is weight. I would like to know the specific example where 1:3 means 33%. I've never seen in college or industry.(posted 8475 days ago)