How deep is the diamond in minecraft?

Diamond ore can be found in layers 1-15, in small veins of 1-10 ores

8 layers above bedrock is where you can find diamond typically also near lava in big caverns and I think you can find within 1-4 ores

The easiest way to reach the diamond level in PE is to dig down until you hit bedrock. Then go up between 2 and 14 levels. That will put you in the 1~16 range in which diamonds spawn.

Thanks