Just entering one and calculating the other is relatively easy. You could do it with a simple calculated query field. Have the user, for example, always enter inches and have the query always calculate mm.

However, allowing the user to pick which one he wants adds a level of complexity that's going to require programming. You would need to be able to store both values in the table. On the form, when the user selects which value they would prefer to input, I would gray out the other field (and disable it) but still calculate it in the AfterUpdate event so you can have it available.

This is beyond the beginner classes, but I could add it to the TechHelp list if you'd like to see it. The list is pretty long, so it may be a while. I am offering priority TechHelp videos now if you want to jump to the top of the list.

Which video was your Celsius to Fahrenheit converter in?

Forgot about that. LOL: Create Your Own Custom Function