Bread-Bakers v106.n012.6

Baking times for similarly shaped loaves of different sizes are 
related to the cube root of the mass. So, if you double the mass and 
hence the volume the increase in baking time is the cube root of 2 
which my calculator shows as 1.2599 so a doubling in size only 
requires about 25% increase in baking time.

Love
John