Homelab electricity cost calculator

A server that idles at 100 watts costs real money over a year. Most homelab owners know what they bought but not what it costs to run. List each device below with how many you have, the watts it draws and how many hours a day it runs. Add your electricity price per kilowatt-hour from your bill, and an optional percentage for the extra cooling or power loss you carry.

You get the energy used per day, month and year and the cost for each. It is a quick way to decide which box to retire, which to power down overnight, and whether a smaller machine would pay for itself.

How the math works

• Energy per day in kWh is count times watts times hours, divided by 1,000.
• The overhead percentage, if any, is added on top.
• Yearly energy is daily energy times 365. Cost is energy times your price per kWh. The monthly figure is the yearly cost divided by 12.

Use a plug-in watt meter for real numbers. The power supply rating on the label is a ceiling, not what the machine usually draws, and idle draw is often far lower than load.

Worked example

One server at 100 W running 24 hours uses 2.4 kWh a day, which is 876 kWh a year. At 0.15 per kWh that costs 131.40 a year, or 10.95 a month. Two 50 W devices running 10 hours a day with a 10 percent cooling overhead use 1.1 kWh a day.