How much did the average loaf of bread cost in 1912 in u. s.?

About a nickel.

The oldest statistical data I can locate doesn't have information earlier than 1913, but in 1913 the average loaf of bread was shown at 5.6 cents. This was as reported in Historical Statistics of the United States: Colonial Times to 1970 (volume 2), as published by the U. S. Department of Commerce.

Or, as another example, the Denver post reported that in 1912 Hurlbut's--which was then a grocery store in Denver--advertised " six loaves of 'homemade' bread for 25 cents," which would work out as a special price less than 5 cents per loaf for the store's bakery bread. (Source: "A Titanic Difference in the Cost of Living 100 Years Later, The Denver Post, March 16, 2012.)