We'd always recommend using Minecraft enchantments, such as Fortune, to ensure that the diamond blocks you mine give you a greater number of diamonds per ore block.

As of 1.17, and in current version 1.21, diamond ore can be found at y-levels 14 to -63, with the heaviest concentration of diamonds spawning at y-levels -50 to -63.

How to Effectively Strip Mine for Diamonds in Minecraft Diamond Ore can be found anywhere between the Y-Level 15 and below, but Diamond Ore is much more common the lower players dig.

You can find diamonds in Minecraft by digging for them with an iron pickaxe or better at layer 15 or below.