Electricity Cost Calculator

This calculator tells you how much it costs to run any electrical appliance, whether a fridge, a TV, an electric heater or an EV charger, based on wattage, daily usage, and your electricity rate.

kWh stands for kilowatt-hour. It’s the standard unit your power bill is measured in: how much energy a 1,000-watt appliance uses if you run it for one hour. Most utilities charge by the kWh.

The Formula

Daily kWh = (Watts × Hours per day) ÷ 1,000 Daily cost = Daily kWh × price per kWh Monthly cost = Daily cost × 30 Yearly cost = Daily cost × 365

Watts From Amps and Volts

If your appliance shows amps and volts but not watts, multiply them:

Watts = Amps × Volts

A typical North American outlet is 120 V, so a “10 amp” appliance pulls 10 × 120 = 1,200 watts. In the UK and most of Europe, outlets are 230 V, so the same 10 amps would be 2,300 watts.

Typical Appliance Wattages (Reference)

These are approximate. Check your appliance’s nameplate or manual for the exact figure.

Nameplate Watts Are Not Running Watts

The number printed on an appliance is usually its maximum draw, not what it actually uses. A fridge labelled 150 W does not draw 150 W continuously; its compressor cycles, so over a day it averages perhaps a third of that. A “1,500 W” microwave draws that only while cooking, and a laptop charger rated 65 W might pull 20 W once the battery is full.

This is the single most common reason a calculated figure comes out too high. Enter the hours the appliance is actually running, not the hours it is plugged in. For a fridge that means about 7 hours a day, not 24.

If you want a real figure rather than an estimate, a plug-in energy monitor costs about $20 and measures actual kWh over days or weeks. That is the only way to catch cycling loads and standby draw properly, and it usually pays for itself the first time it finds something unexpected.

Electricity Prices (Approximate, Vary by Region and Year)

• US average: ~$0.16/kWh (ranges $0.10 in low-cost states to $0.30+ in California/Hawaii)
• UK average: ~£0.25/kWh (price cap)
• Most of Europe: €0.15 to €0.35/kWh

These change yearly. Check your bill for the actual rate.

Worked Examples

Refrigerator (always on, but cycles ~30%): Effective: 150W × 24 × 0.3 = 1.08 kWh/day At $0.16/kWh: $0.17/day = $63/year

Electric kettle (used 6× a day for 2 min): 3,000W × 0.2 hours = 0.6 kWh/day At $0.16/kWh: $0.10/day = $35/year

Window AC (5 hours/day, 5 months/year): 1,500W × 5 × 150 days / 1,000 = 1,125 kWh per season At $0.16/kWh: $180 per season

A whole-house estimate (3,000W average draw, 8 hours/day at $0.13/kWh): (3,000 × 8 × 30) ÷ 1,000 = 720 kWh/month 720 × $0.13 = $93.60/month

For the year, multiply the daily figure by 365 rather than the monthly figure by 12: 24 kWh/day × 365 = 8,760 kWh, which is $1,138.80. Twelve 30-day months only add up to 360 days, so that shortcut quietly undercounts by $15 a year here. The calculator above uses the 365-day figure.

Standby Power, And Whether It Is Worth Chasing

A single device drawing 5 W on standby uses 43.8 kWh a year, which is about $6.60 at $0.15/kWh. That sounds trivial until you count them: a television, a games console, a soundbar, two set-top boxes, three phone chargers and a microwave clock will between them run a permanent 40 W load and cost more than $50 a year to do nothing. Across a household, standby draw typically runs 5 to 10% of the bill.

Switched power strips solve it for the cluster around a TV, which is where most of it hides.

Where to Save

• Heating and cooling are usually the biggest single line on the bill (40 to 60% in many homes)
• Swapping ten 60 W incandescent bulbs for 10 W LEDs at four hours a day saves about 730 kWh a year, roughly $117 at $0.16/kWh
• Turning heating down by 1°C (about 2°F) saves roughly 10% of the heating portion of your bill. That figure is per degree Celsius, not per degree Fahrenheit, so the US equivalent is closer to 5% per °F.
• Chasing phone chargers while an old electric water heater runs unattended is optimising the wrong end of the problem