Ask the Expert Question-and-Answer Archive

by Ron Joseph

October, 2010

VOC % Conversion

Q. I understand that VOC's have to be tracked by % by weight and not VOC by volume. I have been given a VOC % by volume instead of VOC % by weight for a new coating. Are these numbers equal, or would I have to convert from % volume to % weight? I know that % volume only equals % weight if the specific gravity/density are equal, but I don't know if VOC's even have a density. So my question basically is, does VOC % by volume equal VOC % my weight? Thank you!

A. You are correct that VOC is reported by weight. To calculate the weight of total VOC you will need to go to the MSDS and list the density of each VOC ingredient and convert each one from volume to weight.

However, the vendor is obliged to tell you the VOC by weight per EPA Method 24. That is the only method that is legally acceptable and you should not need to perform any caluclations. Since many MSDS only provide approximate weight or volume percentages for each component, it is entirely possible that your calculations will result in an incorrect value. If it is important that you have the correct VOC and if the vendor does not provide that information, it might be worth your while to send a sample to a coating's lab and have them perform Method 24.

Regards,

Ron Joseph