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.)

The answer is About a nickel.

Explanation:

The most established measurable information I can find doesn't have data sooner than 1913, however in 1913 the normal portion of bread was appeared at 5.6 cents.  This was as announced in Historical Statistics of the United States: Colonial Times to 1970 (volume 2), as distributed by the U.S. Branch of Commerce.  Or on the other hand, as another precedent, the Denver post detailed that in 1912 Hurlbut's- - which was then a market in Denver- - promoted "six portions of 'natively constructed' bread for 25 pennies," which would work out as a unique cost under 5 pennies for each portion for the store's pastry kitchen bread.   (Source:  "A Titanic Difference in the Cost of Living 100 Years Later, The Denver Post, March 16, 2012.)

It was basically because people started to stop moving place to place and domesticating animals. Also because of surplus (extra) food