I believe the average upper jaw should be about 44 millimetres for a man and about 42 for a woman. Most people are much less than this and the average width in the UK was 33½ in the1960s and is probably less now. That should be measured at the narrowest point on the gumline of the upper first molars.

Over 90% of people have maxillae that are too narrow and around half of them are less than 33 millimetres, many much less. This is too narrow for you to put your tongue on your palate without contacting the teeth and this is associated with a retruded maxillae, flat cheeks and an apparently big nose although actually it looks big because the cheeks are flat. 

Narrow maxillae also prevent the lower jaw from growing forward giving you a long face, weak chin and narrow jaws. Narrow jaws are not big enough so will result in crooked teeth.

What is the reason. It is caused by our life-style. 1/ Living in houses causes allergies which blocks our noses. 2/ eating soft food shrinks our jaws. 3/ reduced breast feeding results in poor tongue posture.

So what can you do? Most important is to act before the age of 8. If older than that correct your tongue posture and eat harder foods or preferably have orthotropic (growth guidance) treatment with Biobloc appliances. 

Best of luck