4inch (10cm) wide by 28inch (70cm) long allows you to be standing whilst drilling the holes in soil. 
Being a larger auger it is recommend you use a 240v or petrol powered Drill (13mm chuck) with side handle and clutch to protect you against kickback. 
It has a common 13mm (1/2inch) hex head. 

Popular uses are:

• Rapidly planting 4inch potted colour or similar pot size. (Also suitable for planting smaller tubestock where you want to improve the soil by adding compost to the hole)
• Drilling multiple holes and moving sideways between them to cultivate the soil deeply
• Drilling a 100mm diameter tunnel under a path
• Tree Planting and applying fertiliser tablets deep into soil. 
• Post Hole digging to exactly 4inches wide with minimal external soil disturbance. 
• Mixing barrow loads of Concrete/mortar
• Mixing fertiliser into soil mix
• Mixing paint
• Digging a trench for plumbing and irrigation - by drilling holes to required depth consecutively along the line and then remove any remaining soft soil with a trenching shovel or by hand. 

N.B. We hope it is pretty obvious... but we better say it - The price does not include the Dewalt Drill shown in the demonstration images. The Power Planter can fit onto any standard Australian drills with a 13mm chuck. (eg. Ryobi, Bosch, Black and Decker, Hitachi, etc )