Use this tool to calculate how much gravel you need for your gravel grids.
This calculator offers two different depths, depending on whether you want to see the grids ("flush") or not ("hiding").
How much 10mm-20mm size gravel you will need:
Flush with top of grid: 80kg
Hiding the grid: 120kg
Typically, you would need between 20kg-30kg of 10-20mm gravel per IBRAN-X gravel grid.