Here is a chart showing the common sizes. You can do the math to convert to O. I use Black Beauty fine for "Chestnut", (the most common size), and the coarser grit for "Stove" coal.
| Coal Size | Min Size in Inches | Max Size in Inches | Similar Sized Objects |
|---|---|---|---|
| Barley | 3/32" | 3/16" | Coarse Sand |
| Rice | 3/16" | 5/16" | Pencil Eraser |
| Buckwheat(Buck) | 5/16" | 9/16" | Dime |
| Pea | 9/16" | 13/16" | Quarter |
| Chestnut(Nut) | 13/16" | 1-5/8" | Golf Ball+ |
| Stove | 1 5/8" | 2 7/16" | Baseball |
| Egg | 2 7/16" | 3 1/4" | Softball |
| Range* | 9/16" | 1-5/8" | Quarter to Baseball |
