3M offers a test strip for measuring FFA% of oil. The strips cost about 50 cents a strip and will quickly tell us roughly how good or bad your oil is. It's a great idea for when your scouting for sources and want to test the oil on site.

They have two different strips. The "Normal Range" strips have four steps from 7% FFA. That's NaOH titrations ranging from 2.6 to 9.1. The "Low Range" strips have four steps from 2.5% FFA. That's like NaOH titrations ranging from 1.3 to 3.2.

3M recommends using them when the oil is at operating temperature,  but hobbyists  have tested it on room temperature oil and found the strips are just as accurate at room temperature. They do however take several minutes instead of several seconds to completely change colors.

One other note is they only have a one year shelf life, so don't buy more than you can use in a year. Someone suggested keeping them in the frig or freezer, but I don't know if that is necessary or not.

Related Links:

3M Oil Quality Test Strips - amazon.com

Testing for FFA - Frybrid forum thread 

3M Brochure .