The Bond Ball Mill Work Index (BWi) test is used to determine the net power requirements to grind a specific ore reducing its feed size (80% passing, F80) to a product size (80% passing, P80). The normal finishing size of this closed circuit dry grindability test is typically 150 microns, but other sizes can be selected based on process requirements. The method uses a standard Bond ball mill and grinding media. This test requires a minimum of 6 kg of sample with a feed size of 100% passing 3.36 mm. There is a modified version of the Bond Ball Mill test. The modified test requires calibration against the standard test but can be used to profile large ore bodies.