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Running a 100 W office PC 8 h/day costs about $42 a year

A 100 W office PC running 8 hours a day at 60% load costs about $31.54 a year at $0.18/kWh — $2.63 a month. That's 175 kWh annually; at scale (say 500 seats) it's 87,600 kWh and $15,770 a year, which is when enterprise IT starts caring about specifying efficient Mini PCs instead of full towers.

Annual cost
$32
At $0.18/kWh
Monthly cost
$3
8 h/day at 60% load
Annual consumption
175 kWh
100 W rated

Calculator

Power Cost Estimator

Device Configuration

W

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Effective Power: 60W

Hours
$/kWh

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Daily Cost
$0.09
Monthly Cost
$2.59
Yearly Cost
$31.54
175 kWh / year

How this is calculated

A "100 W" office PC is the PSU rating — actual desktop draw for light office work is typically 25-45 W with occasional bursts to 70 W during compiles or video calls. The 60% utilisation figure here is calibrated to capture that mix across an 8-hour day, including lunch and meetings where the machine is mostly idle. Aggressive sleep policies can reduce this further, though in a business context the trade-off with user productivity typically keeps machines awake.

Verdict

$32 per year per seat is trivial individually but compounds quickly at scale. For 1000+ seat fleets, switching from 100 W towers to 45 W thin-client Mini PCs is a $17k/year operating expense cut on electricity alone.

Frequently asked questions

How much does it cost to run a gaming PC 24/7?
At 300 W continuous draw and €0.30/kWh, a gaming PC left on 24/7 costs about €788 per year. Cut that to 8 hours per day of active gaming plus idle the rest and it drops to roughly €260/year. Sleep mode and turning the PC off when not in use are the biggest levers.
How do I calculate kWh from watts?
Multiply wattage by hours, then divide by 1,000. A 500 W device running for 4 hours uses 500 × 4 ÷ 1,000 = 2 kWh. Multiply by your electricity rate (e.g. €0.30/kWh) to get the cost.
What uses more electricity: an RTX 4090 or a typical fridge?
Peak power, the RTX 4090 wins (450 W vs roughly 100-150 W compressor draw). Annual consumption is the opposite: a fridge runs 24/7 at an average of 40-50 W, adding up to around 400 kWh/year — more than many gaming PCs used only a few hours daily.
Does a 1000 W PSU use 1000 W all the time?
No. A PSU is rated for its maximum output capacity; actual draw depends on what the components need. A system with a 1000 W PSU at idle might pull 80 W from the wall, jumping to 400-600 W under gaming load.
How much does an always-on TV or server cost per year?
At 100 W continuous draw and €0.30/kWh, any device running 24/7 costs €263/year. A home NAS at 50 W costs €131/year; a 65-inch OLED TV watched 4 hours/day at 150 W costs about €66/year.
Why is my electricity bill higher than the estimator predicts?
The estimator assumes the wattage you enter is the average over runtime. Real devices spike, idle, and have standby draw. Measure with a cheap wall-socket power meter for the most accurate baseline, then use the estimator to project costs for different usage scenarios.

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