What is a kilowatt-hour and how do I work out how many my rig uses?

A kilowatt-hour (kWh) is the unit your electricity company bills in: one kilowatt of power used for one hour. To find your rig's daily kWh, take its measured wattage, multiply by hours run, then divide by 1,000. A 400W rig running 24 hours uses 400 times 24 divided by 1,000, which equals 9.6 kWh per day, or roughly 288 kWh a month. Multiply that by your effective rate per kWh to get the cost. This is the single most important calculation in home mining, because every cost estimate flows from it. Always use your real measured watts, not the number printed on the power supply label.