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Mini PC electricity calculator
Defaults are examples, not measurements or a current tariff. Invalid entries leave the last valid result in place.
365-day year; monthly average = annual ÷ 12. Excludes purchase price and standing charge. Calculations stay in your browser.
1. Enter the three numbers that matter
| Calculator input | What to enter | Avoid this mistake |
|---|---|---|
| Average socket power | A measured average for the PC and devices you want to include | Using the adapter's maximum output or the CPU's power rating |
| Hours per day | 24 for an always-on server | Entering only the hours you actively use it while it stays powered on |
| Electricity rate | Your bill's unit rate in pence per kWh | Entering 0.25 when you mean 25p |
The initial 15W and 25p rate are examples. The calculator uses a 365-day year and excludes the standing charge on an existing electricity supply.
2. Measure watts, or work with a range
Already own the PC? Put a suitable plug-in energy meter between its power adapter and the socket. Record kWh over several ordinary days, including backups and other scheduled jobs.
Average watts = recorded kWh × 1,000 ÷ hours measured.
For example, 1.08kWh over 72 hours = 15W average. A quick idle reading can miss work that happens overnight. Intel's CPU power figures describe the processor, so do not substitute them for a whole-PC measurement.
Haven't bought it yet? Try 10W, 20W and 30W. These are sensitivity checks, not claims about the machines in our shortlist. If the buying decision changes across that range, you need better power evidence before paying a premium for efficiency.
3. See the size of the bill
At an illustrative 25p/kWh, running 24 hours a day:
| Assumed average power | Electricity per year | Electricity over three years |
|---|---|---|
| 5W | £10.95 | £32.85 |
| 10W | £21.90 | £65.70 |
| 15W | £32.85 | £98.55 |
| 20W | £43.80 | £131.40 |
| 30W | £65.70 | £197.10 |
The calculation is watts ÷ 1,000 × hours/day × 365 × pence/kWh ÷ 100. The monthly result is the annual cost divided by 12; it is an average, not a prediction of a particular month's bill.
4. Decide whether lower power is worth paying for
At that rate, saving 5W saves £10.95 a year. Paying £100 extra for a genuine 5W reduction takes about 9.1 years to recover through electricity alone. Over three years, the energy saving justifies a premium of £32.85, before considering warranty, performance or repairs.
Use this rule: maximum premium justified by energy = annual saving × years you expect to keep it. Compare the final purchase prices in the used-versus-new guide.
If your tariff or operating hours vary
For a time-of-use tariff, calculate each daily rate period separately and add the annual results before rounding. Example: 20W for 7 hours at 10p plus 17 hours at 30p costs £42.34 a year.
If the PC sleeps outside the hours entered, calculate its standby consumption separately. The hours field assumes zero use for the rest of the day.
Sources and review date
Source dates are listed below. Recommendations are our editorial judgement; we have not physically tested these machines.
- Intel: Core 3 100U power specifications ↗ · 8 Sept 2026
- Energy Saving Trust: time-of-use tariffs ↗ · 8 Sept 2026