Is there a formula for the amount of space a video will take based on fps and resolution?

I’m sure there is, but does anyone know this?

I was wondering how much minutes of video you could get when using a 720×480 resolution camera at 25fps with a 20gb memory card. I haven’t bought the camera yet which is why I am asking this question. Also it may be useful for future knowledges.

I was hoping to get the formula in terms of time but don’t mind other ways as I can probably rearrange if you just know the formula and can copypasta.

So the variables I am interested in are: time, fps, resolution and memory.