Work index is defined as the

• gross energy (kWh/ton of feed) needed to reduce very large feed to such a size that 80% of the product passes through a 100 micron screen.
• energy needed to crush one tonne of feed to 200 microns.
• energy (kWh/ton of feed) needed to crush small feed to such a size that 80% of the product passes a 200 mesh screen.
• energy needed to crush one ton of feed to 100 microns.