How many hour is normal sleeping?

8 to 10 usually: This is a very specific question. Some do well with 7 to 8 hours, some need 10 or more. If you find that you are refreshed in the morning then you are getting plenty whatever the number. If you are getting upwards of 10 or more and still feel tired, then a discussion with your doc may be warranted. Thyroid or obstructive sleep apnea may be possible.

7 hours: Depends on your age, young vs old, 6 to 7 hours, need to avoid some medical problem in the future( hypertension, depression, dm).

Varies: This varies with age and activities. A mature adult should with good sleep habits can usually get by with 6-8 hours. Physical activity (work or play), intense reading or thinking work would add need. Any illness will add some need as would extra stresses at work.