With negative it's all relative, there is no specific point that can be defined as the absolute middle gray point. This is because print exposure is set in the enlarger, and in the enlarger you can place any tone you please from the film at middle gray on the paper.
Proper metering allows you to set the camera in a way that allows you to get good shadow and highlight detail around middle gray. It gives you a reference point to make your work easier.
If for example you used TMY which has a 14 stop range you could pick an EI that might put your intended middle gray 7 stops above the film's toe. 1 or 7 stops to the toe, it's your choice.