PC electricity cost

How much does your PC actually cost in electricity?

Watts on a spec sheet don't mean anything until you turn them into a number on your bill. Here's the watts-to-kWh-to-money formula, why the answer changes if you're on a time-of-use (peak/off-peak) rate plan, and how to have the math done for you hour by hour instead of guessing with one flat rate.

Quick answer: kWh = (watts ÷ 1000) × hours running, then cost = kWh × your price per kWh. A PC averaging 150 W for 8 hours a day at $0.15/kWh runs about $65.70/year. If your utility charges different rates at different times of day (time-of-use / TOU), you need to split those hours apart first — a flat multiplication will be wrong. Read on for the TOU math and how to automate it.

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The formula: watts to kWh to dollars

Electricity bills are priced in kilowatt-hours (kWh), not watts, so the first step is always a unit conversion. Three numbers, in order:

Energy used: kWh = (watts ÷ 1000) × hours running. A PC drawing 150 W for 8 hours uses (150 ÷ 1000) × 8 = 1.2 kWh that day.
Over a year: multiply by days used. 1.2 kWh/day × 365 ≈ 438 kWh/year for that same machine.
Cost: cost = kWh × price per kWh. At a flat $0.15/kWh, 438 kWh ≈ $65.70/year. Swap in your own wattage, hours, and rate and the number moves accordingly.

The watts figure matters most. A gaming PC pulling 350 W under load costs roughly 2.3× as much per hour as one idling at 150 W. So where that number comes from changes the answer more than the rate does. A plug-in meter is the most accurate source; software CPU+GPU estimates run a bit low, since they miss the motherboard, RAM, storage, and PSU conversion loss.

Why a flat rate isn't the whole story

The watts-to-kWh-to-money formula assumes one price per kWh no matter when you used it. That's true for a flat-rate electricity account — most residential plans work this way. But a growing number of utilities charge a different rate depending on the hour: more during peak demand, less off-peak. In Taiwan, Taipower's time-of-use (TOU) plans work this way, but residential accounts are on tiered (progressive) rates by default, and TOU is an opt-in plan. On a TOU plan, the exact same 1.2 kWh can cost noticeably more or less purely based on when your PC drew that power — the single-multiplication formula will be wrong unless you split the hours apart first.

Rate structure	How it's priced	What you need to calculate cost
Flat rate	One price per kWh, all day, every day	Total kWh × the one rate
Time-of-use (TOU)	A higher rate during peak hours, lower off-peak; summer and non-summer peak hours differ	kWh used in each time band × that band's rate, then added together
Automated hour-by-hour	PowerDoze applies your rate schedule automatically	Nothing — it multiplies every hour of measured usage by that hour's rate for you

Taiwan: peak/off-peak and Taipower's rate structure

Taipower (台電) has a simple time-of-use plan whose two-tier version makes a good example (prices in effect since October 1, 2025). On weekdays the peak window is 09:00–24:00 in summer (June 1 to September 30) at NT$5.16/kWh, and 06:00–11:00 plus 14:00–24:00 the rest of the year at NT$4.93/kWh. Everything else is off-peak (NT$2.06/kWh in summer, NT$1.99/kWh otherwise), and Saturdays, Sundays, and national holidays are off-peak all day. Time-of-use accounts also pay a basic charge of NT$75 a month. Other Taipower plans, such as the three-tier version, use different hours and prices, so check your own bill or Taipower's rate table for your numbers.

Why weekends and holidays matter to the math

Most TOU plans bill all day Saturday and Sunday at off-peak, and the same goes for national holidays (New Year's Day, Lunar New Year, Peace Memorial Day, Children's Day, Tomb Sweeping Day, Dragon Boat Festival, Mid-Autumn Festival, National Day, and others). That means the same 10am usage can cost two different amounts. On a Tuesday it's billed at the peak rate, but if that Tuesday falls on a holiday, it's billed at the lower off-peak rate. It's an easy detail to forget when estimating a whole year by hand.

Best for: Anyone estimating annual cost who wants to know why a rough "weekday = peak" assumption overcounts. Note: Holiday dates shift every year (especially the lunar-calendar ones), so a fixed list needs updating annually to stay accurate.

Doing the TOU math by hand

If your PC runs 24 hours a day at a steady 150 W on that two-tier plan outside summer (weekday peak 06:00–11:00 and 14:00–24:00, 15 hours at NT$4.93/kWh; off-peak NT$1.99/kWh), weekday cost looks like this:

Split the day, then add

Peak hours (15 hours): (150 ÷ 1000) × 15 × 4.93 ≈ NT$11.09. Off-peak hours (9 hours): (150 ÷ 1000) × 9 × 1.99 ≈ NT$2.69. Total for that weekday: ≈ NT$13.78. On a weekend or holiday, the whole 24 hours falls to off-peak: (150 ÷ 1000) × 24 × 1.99 ≈ NT$7.16 — noticeably less for the identical usage.

Best for: A one-off estimate or sanity-checking a bill by hand. Note: This gets tedious fast for a variable load (a PC's wattage swings by workload, not a flat 150 W), which is where doing it per actual hour of measured usage instead of an assumed average pays off.

Doing it automatically, hour by hour — PowerDoze (Pro)

Splitting peak and off-peak hours by hand every day isn't realistic when your PC's wattage changes all day (idle, gaming, a render job at 2am). PowerDoze's electricity rate settings let you enter either a single flat rate or a full time-of-use schedule: an off-peak rate plus your own custom peak windows, with weekends and national holidays automatically treated as all-day off-peak. The built-in defaults (NT$1.85/kWh off-peak, weekdays 10:00–17:00 at NT$4.44/kWh) are only an example, not Taipower's current prices, so replace them with the numbers on your bill. One set of hours and rates applies all year; Taipower's summer and non-summer schedules differ, so update it when the season changes. It then multiplies every hour of your PC's measured or estimated power draw by that hour's rate and adds it up — instead of one flat number applied to your whole day. Works in 7 currencies (TWD, USD, EUR, JPY, KRW, CNY, GBP), so it's not Taiwan-only.

Honest note: This is a simulation of the rate structure you enter, not a live read of your Taipower account — your actual bill is the source of truth, and PowerDoze's number is for tracking and comparison, not a substitute. Requires Pro. Free users still see PC power usage; the rate-schedule math (fixed and TOU) is a Pro feature.

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Frequently asked questions

How do I calculate how much my PC costs in electricity?

Convert watts to kilowatt-hours, then multiply by your rate: kWh = (watts ÷ 1000) × hours running, then cost = kWh × price per kWh. A PC averaging 150 W for 8 hours a day at $0.15/kWh works out to (150 ÷ 1000) × 8 × 365 × 0.15 ≈ $65.70 a year. Swap in your own wattage, hours, and rate.

How do I convert kWh to a dollar amount?

Multiply the kWh figure by your price per kWh from your electricity bill. If you don't know your rate, it's printed on your bill as a price per kWh (or per 度 in Taiwan) — flat-rate accounts have one number; time-of-use accounts have a different rate for each time band, so the same kWh costs more or less depending on when it was drawn.

Does it matter what time of day my PC uses power?

Only if you're on a time-of-use (TOU) rate plan. Flat-rate accounts charge the same price no matter the hour, so timing doesn't change the bill. TOU accounts charge more during peak hours and less off-peak, so the exact same kWh can cost noticeably more if it's drawn at 2pm instead of 2am.

What are Taiwan's peak and off-peak electricity hours?

Take Taipower's simple time-of-use plan, two-tier version (prices in effect since October 1, 2025). On weekdays, peak is 09:00–24:00 in summer (June 1 to September 30) at NT$5.16/kWh, and 06:00–11:00 plus 14:00–24:00 the rest of the year at NT$4.93/kWh. Every other hour is off-peak, at NT$2.06/kWh in summer and NT$1.99/kWh otherwise, and Saturdays, Sundays, and national holidays are off-peak all day. Taipower's other plans, such as the three-tier version, use different hours and prices, so check your bill or Taipower's rate table for your own numbers.

Can software calculate my real electricity cost automatically?

Yes, if it tracks your PC's power draw over time and can apply a rate per hour rather than one flat number. PowerDoze does this: enter either a single flat rate or a time-of-use schedule with peak/off-peak bands, and it multiplies each hour's measured usage by that hour's rate automatically, in 7 currencies.

Is the cost PowerDoze shows my actual electricity bill?

No — it's a calculation based on the rate schedule you enter and PowerDoze's own measured or estimated power draw, not a read of your utility account. Treat it as a close simulation for tracking and comparison, not a substitute for your actual Taipower (or other utility) bill.

Want your PC's real cost calculated hour by hour instead of estimated with one flat number? PowerDoze Pro applies your own flat or time-of-use rate schedule automatically, in 7 currencies.