Block Size, Rotation and Texture Window Versions MCreator 1.5.2 to 1.9.0 Overview In the first window for block creation you have the option to resize the block hit box or if its a default block with no custom model you can resize the dimensions of the block with its hit box. Below are a few charts to help with resizing the blocks. Minimum default cords are always set to 0, and Maximum default cords are always set to 1, the number ranges between 1.0 and 0.0. Each pixel in Minecaft is 0.0625. To use the chart below look at the pixel tab then scroll down until you reach the amount of pixels you want the minimum cords to be sized to. Once you have located the pixel then your value is under the MCreator size for what you need to use in MCreator. On the right of that cell is the actual size of the pixel in real Minecraft. Due to MCreator only accepting values with three decimals you are not able to use the exact pixel size, you will need to round the value to the three decimal value to the closet value available. Example of Custom Dimensions For a 12 x 16 x 12 size is below. Reference to the charts below to lean how to use the chart. Increase the values on for minimum sides to decrease the size of the block. Decrease the values on the maximum sides to decrease the size of the block. 
Min X = 0.125 (-2 px) Min Y = 0.0 (default) Min Z = 0.125 (-2 px) Max X = 0.875 (-2 px) Max Y = 1.0 (default) Max Z = 0.875 (-2 px) Block Dimensions for Minimum Values Only use these for Mix (X, Y or Z) values. Block Dimensions for Maximum Values Only use these for Max (X, Y or Z) values.