I can't remember the exaxt numbers when i filled mine up but I have 3 layers:
1. Drainage with hydrospheres max. 40L. Ricoter Blähton (25l, Hydrokugeln)
2. The drainage layer was then separated with a fleece which lets the water through, but stoppeds the earth coming into the drainage
3. A layer with universal soil (Auffüllerde) because it is cheaper. I would say around 250-280L
4. After that just fill up the rest with potting soil. We looked that there is about 15cm of potting soil.

In the end i had one 70L of universal soil left but after a while it sank in. https://imgur.com/a... You can see in the image that it isn't filled up completely.

Hope that helps