I have vegetable oil but my recipe calls for olive oil. Will it make a difference to use the vegetable oil? Also, what would the conversion be? I'm trying to make a homemade pizza crust without yeast and this oil situation has me stumped.
You can substitute vegetable oil for olive oil, that is no problem. You won't have the flavor that olive oil brings to the party, but in the case of more refined (not extra virgin) olive oils, it really won't make much difference. Just use however much oil the recipe calls for. It'll be fine.
The main difference will be the flavor. Especially cold pressed extra virgin olive oil can add an extra twist of flavor depending on quality, variety and source. Quantity can be substituted one to one as every cooking oil has pretty much the same consistency and density.
In the case of making pizza dough, switching olive oil for vegetable oil will only change the flavor of the final product. The conversion is 1-to-1.
In other cases it can make a difference; for example refined olive oil has a higher smoke point than vegetable oil, which in turn has a higher smoke point than (extra-)virgin olive oil.
Substituting vegetable oil for olive oil will make no difference in pizza dough. I would substitute it 1:1. They are not, however, interchangeable in other circumstances.Olive oil can add more flavors to a dish than vegetable oil, and it also burns at a lower temperature so is unsuitable for frying. I enjoy its flavor and think that vegetable oil brings a more oily texture/taste, but that could be purely personal preference. Good luck!