There is a range in the amount you can store, and it's based on the frame rate. Higher frame rates will use more space. To get an idea of how much you can record in pN mode, change the frame rate and you will see the number of minutes of available recording time change in the upper right of your LCD, to the left of the battery indicator.
And don't forget that if you're in 24pN mode using a frame rate other than 24 fps, you won't record any audio (same goes for 30pN and rates other than 30 fps).