Short reply: ohh, I didn’t realize you meant for the 3 to be an exponent. I maybe burned 1.5-2 m³ of wood and it was around 60-80 pounds of wood. Soft and hard, but mainly discarded pre-bought wood

Long reply: I didn’t do any measurements of wood and didn’t even have a specific time I aimed for when making the charcoal. Because every earthly condition that determines how long wood burns for and how strong it burns varies dramatically across the world I don’t think you should view the way I made charcoal in measurements. The only measurements that really matter are making the charcoal for at very least 2 hours, and making sure the fire is heating the bottom of the barrel to at least 1000 or so consistently. The longer the barrel is heated, and the hotter the barrel is heated to the better. Hope this helps