OK I think with the help of google I found the volume of ash produced by Kingsford - I figure if it can hold that any lump or better fuel would be a snap
Originally Posted by http://www.nakedwhiz.com/productreviews/kvsk/oldkingsfordnew.htm
What About Ash Production?
The Test: Kingsford doesn't make any claims about the volume of ash produced by these two types of briquettes that we can see, but part of our regular testing of lump charcoal is to measure the volume of ash produced. This can be important in some types of cookers because the ash can block air vents and affect the fire. Basically, after the burntime time test is finished, we open the lid of the cooker and let all the charcoal burn to ash. Once it is cooled, we measure the volume of ash in a graduated vessel.
The Results: 3 pounds of the old briquettes produced 850 ml of ash, while the new briquettes produced 875 ml of ash.
Conclusion: This test only reaffirms that both the old and new briquettes produce an appalling quantity of ash.
So 12 Lbs would produce 3500 milliliter = 213.59 cubic inches of ash