In Minecraft, a full beacon requires a 3x3 square of blocks to be placed underneath it as its base. This means you need a total of 9 blocks to form the pyramid base for the beacon.

Additionally, to activate the beacon and unlock its full powers, you must also construct a pyramid of certain specified blocks above the beacon base. The number of layers in the pyramid and the type of blocks used determine the beacon's powers and range.

Here's a breakdown of the required blocks for a full beacon pyramid:

- For the first layer above the base (second layer overall), you need 9 blocks.

- For the second layer above the base (third layer overall), you need 9 blocks.

- For the third layer above the base (fourth layer overall), you need 9 blocks.

- For the fourth layer above the base (fifth layer overall), you need 1 block.

So, in total, constructing a full beacon requires 9 (for the base) + 9 (for the second layer) + 9 (for the third layer) + 1 (for the fourth layer) = 28 blocks.