No magic number. In general, drinking one standard drink per day (5 oz wine, 1 1/2 oz liquor, 12 oz beer)or 7 drinks/week in women and men over 60 is not associated with liver injury. However, there are genetic factors, and some people are way more sensitive. Amounts about twice the above are needed for any injury, and usually 3-4 x those amounts for serious injury. If you have hep c, any amount of alcohol is bad.
Cirrhosis & alcohol. Cirrhosis is scarring of the liver. It can occur without any alcohol consumption at all. Alcohol can exacerbate another condtion making it progress to cirrhosis more quickly. Most 'true' alcoholics' do not develop cirrhosis without someother condition present. Cirrhosis purely due to alcohol is relatively uncommon. Hepatitis from alcohol can mimic cirrhosis yet fully recover with abstinence.