If you are referring to academics, you can expect that formulae will be used. These two actually refer to the same thing but the only difference is that formula will be used when you are referring to something that is singular while you are going to use formulae when you are referring to something plural. The word “formula†is a Latin word but it became absorbed into the English language by the 1600s. The word “formula†was used to refer to things that are related to ceremonies and rituals. Right now, this is used to mean that there are certain things that would require a specific combination in order to work properly.
It can be confusing for some people to encounter the world formulae, especially if they have been using the word formulas all their life. When you need to use more than one formula, you are going to use the term “formulae†which will signify that there is more than one formula. In other words, this is the plural form of formula. Over the past years, “formulas†have started to become more accepted, although if you would like to be more grammatically correct about it, using “formulae†can be the better option. For those who are not aware, the formula is a Latin word that also started to become used and accepted in the English language.