⚡ What does the server really cost?
A server running around the clock costs more to operate than to buy — at 100 watts of continuous load that is roughly 300 euros per year depending on your tariff, year after year. The maths is simple multiplication, yet almost everyone looks at only half the equation: they forget cooling and they use the nameplate rating of the power supplies.
The formula in three lines
Power: P_total = measured watts × PUE. Energy: kWh = P_total × hours per day × 365 ÷ 1000. Cost: € = kWh × price per kWh.
Example: 100 watts, 24 hours a day, 35 cents per kWh give 876 kWh and 306.60 euros per year. With a PUE of 1.3 — a server room where cooling adds 30 percent on top — it becomes 1,139 kWh and 398.58 euros. That single line is missing from most calculators.
The three classic mistakes
- Netzteil-Nennleistung statt Messwert: Ein 750-Watt-Netzteil zieht selten über 400 Watt. Wer die Nennleistung ansetzt, überschätzt die Kosten um den Faktor zwei bis drei — und kauft zu große Hardware.
- Kühlung vergessen: Jede Kilowattstunde im Server wird im Raum zu Wärme und muss wieder hinaus. Im Serverraum kommen 20 bis 50 Prozent hinzu, deshalb der PUE-Faktor.
- Idle mit Last verwechseln: Ein Homelab-Server zieht im Leerlauf 40 Watt und unter Last 180. Der ehrliche Wert ist der Durchschnitt über den Tag, nicht der Spitzenwert.
What you need the power cost calculator for
You want to know whether a more efficient server or CPU really pays off — a question that can only be answered with your electricity price, not with datasheets. Or you are planning the running cost of a small rack and need a monthly figure rather than a kilowatt hour. That is exactly why there is a second calculation here: enter the purchase price plus the old and new power draw, and you see after how many years the purchase has earned its money back. Everything runs in your browser, your consumption data never leaves the machine.
How to use the calculator
Measure the continuous draw of your hardware — with a plug-in power meter, the UPS display or the value from your PDU. One measurement under typical load is enough.
Enter the electricity price and the operating hours. A server runs 24 hours; backup and test systems often only a few hours per day.
Pick the PUE that matches the location: 1.0 for living space, 1.2 for a small server room, 1.5 and above when air conditioning removes the heat.
For the payback, enter the power of the old and the new hardware plus the purchase price. The rule of thumb for your thumb: 1 watt of continuous load costs about 8.8 kWh and therefore roughly 3 euros per year.
Worked example: two old servers versus one new one
Two old machines draw 120 watts together; a new server needs 40 watts and costs 600 euros. At 35 cents per kWh and 24 hour operation the upgrade saves 701 kWh and about 245 euros per year — paid for after roughly two and a half years, and purely profitable afterwards. What matters is honesty about the measurements: use the PSU stickers instead of real readings and every payback looks better than it is.
Frequent questions
What is the PUE value?
PUE stands for Power Usage Effectiveness and describes how much electricity is added on top of the IT load for cooling, losses and auxiliary systems. 1.0 means no overhead (living space). A classic server room sits at 1.3 to 1.6, older installations higher.
Should I use the measured or the vendor value?
Always the measurement. Vendor figures are maximums or idle values, never the typical mixed workload. A 20 euro power meter gives you the only number you can calculate with.
Why does the calculator use 365 days?
Because servers run continuously. The annual figure is the most honest number for running costs, because it does not blur price changes or partial months. If you only need the monthly cost, it sits right next to it in the table.
How accurate is the CO₂ figure?
It is an estimate using the grid factor you enter — 380 grams per kilowatt hour is pre-filled as a guide for the German mix. If you buy green power, set it lower; the figure is about order of magnitude, not about certified accounting.
Does the calculator include the UPS?
No — the UPS sits behind the load and converts with losses. For UPS runtime use the UPS calculator. For electricity cost what counts is the power actually drawn from the socket, including the losses a plug-in meter shows anyway.
Sources & further reading
The formulas and factors follow common running-cost practice (power draw × operating hours, PUE as the cooling factor). To plan the full hardware chain: UPS calculator, IOPS calculator, RAID calculator and the capacity converter. Background in the blog: SSD lifespan and storage tiering.
⚡ Continue with the UPS calculator — or the download time.