Appliance Wattage Calculator · Watts, kWh & Running Cost

Appliance Wattage Calculator

Find how many watts any appliance uses and what it costs to run

Currency
Appliance
units
Quantity multiplies the wattage and total cost — useful for identical items like light bulbs or fans.
Power
W
Not sure of the wattage? Check the appliance label for W, or multiply volts × amps. For ACs, 1 ton ≈ 3,517 W of cooling ≈ 12,000 BTU/h.
Usage
h / day
d / week
w / year
%
Duty cycle is the % of the "on" time the appliance actually draws full power. Fridges ~30–40%, ACs ~50–70%, continuous loads (TV, PC) 100%.
Electricity & CO₂
$ per kWh
CO₂ intensity varies widely by grid. Choose your region or pick None to hide carbon estimates.
Wattage & Consumption
🔌 Low Power Draw
Appliance wattage
—
—
Per day of use
—
Per week
—
Per month
—
Per year
—
Cost per year
—
Cost per month
—
Cost per day
—
CO₂ per year
—
Energy & cost breakdown
PeriodHours usedEnergy (kWh)CostCO₂ (kg)
Estimates use the wattage, duty cycle and schedule you entered. Real consumption varies with appliance age, ambient temperature and how you use it.
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Faiq Ur Rahman

Founder & CEO, Toolraxy

Faiq Ur Rahman is a web designer, digital product developer, and founder of Toolraxy, a growing platform of web-based calculators and utility tools. He specializes in building structured, user-friendly tools focused on health, finance, productivity, and everyday problem-solving.

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The label on the back of an appliance tells you its wattage. What it doesn’t tell you is what that number costs. A 1,500 W space heater and a 1,500 W kettle use the same power but for wildly different amounts of time. This calculator bridges the gap. It converts raw wattage into kilowatt-hours, applies a duty cycle to account for appliances that cycle on and off, and multiplies by your electricity rate. The result is a yearly cost figure you can compare against the next appliance you’re considering. Useful for budgeting, for comparing energy ratings, and for spotting which device is driving up the bill. Everything runs locally.

 

How to Use the Appliance Wattage Calculator

  1. Choose your currency from the dropdown at the top.

  2. Name the appliance and set how many identical units you’re calculating.

  3. Pick a power input method. Watts is the default for most appliances.

  4. Enter the wattage, or fill in volts and amps, or type the BTU/h figure for an air conditioner.

  5. Set hours per day, days per week, and weeks per year to match your usage pattern.

  6. Add a duty cycle if the appliance cycles. A fridge runs about 35% of the time it’s plugged in.

  7. Enter your electricity price per kWh.

  8. Read the annual cost in the results panel.

  9. Check the breakdown table for per-day, per-week, per-month, and per-year energy use.

 

How the Appliance Wattage Calculator Formula Works

The calculation chains power, time, and price together.

Formula: Watts = Volts × Amps × Power Factor
Formula: Watts = BTU/h ÷ 3.412142
Formula: Effective watts = Watts × Duty cycle %
Formula: kWh = (Effective watts ÷ 1000) × hours of use
Formula: Yearly kWh = kW × hours/day × days/week × weeks/year
Formula: Cost = kWh × price per kWh
Formula: CO₂ = kWh × grid intensity (kg/kWh)

Each power input method produces the same unit wattage before the rest of the math runs. Direct watts is the simplest. Volts × amps matters when the label lists voltage and current separately. Power factor adjusts for inductive loads like motors, where current and voltage don’t peak together. BTU/h converts to watts at 3.412142 BTU per watt, so a 12,000 BTU air conditioner draws about 3,517 W of cooling capacity, though actual electrical draw is lower because ACs move heat rather than generate it.

Duty cycle handles appliances that cycle. A fridge compressor runs about 35% of the time it’s plugged in. An air conditioner might run 65% of the time during peak cooling. Continuous loads like a TV or a PC sit at 100%. The calculator multiplies raw watts by the duty percentage to get the average draw.

Validation requires positive wattage. Other fields fall back to defaults if left blank. The badge classifies total wattage: under 100 W is low, 100 to 500 W is moderate, 500 to 1,500 W is high, and above 1,500 W is very high.

 

Worked Example

A chest freezer in a UK home draws 120 W. It runs 24 hours a day, 7 days a week, all year. The compressor duty cycle is 35%. UK electricity costs £0.24 per kWh.

Effective watts: 120 × 0.35 = 42 W
Yearly kWh: (42 ÷ 1000) × 24 × 7 × 52 = 366.9 kWh
Yearly cost: 366.9 × 0.24 = £88.06
Monthly cost: 88.06 ÷ 12 = £7.34
Daily cost: 88.06 ÷ 365 = £0.24

Carbon at the UK grid intensity of 0.233 kg/kWh: 366.9 × 0.233 = 85.5 kg CO₂ per year.

The badge reads “Moderate Power Draw” because 120 W sits in the 100-to-500 band. The same chest freezer run on a French grid (0.052 kg/kWh) would emit just 19 kg CO₂ per year, a fifth of the UK figure.

Now swap the freezer for a 3,000 W tumble dryer used twice a week for one hour at 90% duty. Effective watts: 2,700 W. Yearly kWh: 2.7 × 1 × 2 × 52 = 280.8 kWh. Cost at £0.24: £67.39. Fewer running hours but more power per hour, which is why appliance choice matters as much as usage pattern.

Frequently Asked Questions

How do you calculate wattage?

Multiply volts by amps for a DC circuit or a resistive AC load. For AC motors and electronics, multiply volts × amps × power factor. If you only have BTU/h, divide by 3.412142. The calculator accepts all three input methods and produces the same effective wattage for the rest of the calculation.

 

How many watts does a refrigerator use?

A modern fridge draws 100 to 200 W while the compressor runs, but it cycles at about 35% duty. Average draw works out to 35 to 70 W continuously. Older fridges can peak at 300 W or higher. Enter the rated wattage and set duty cycle to 35% for an accurate yearly figure.

 

How much does it cost to run a 1,500 W space heater?

At £0.24 per kWh, running a 1,500 W heater for 4 hours a day costs about £1.44 daily, £43.20 monthly, and £518 yearly if used year-round. Winter-only use over 5 months drops the yearly figure to around £216. Space heaters are among the most expensive appliances per hour of use.

 

How many watts does an air conditioner use?

A window AC draws 900 to 1,500 W. A split system for a whole room sits at 1,500 to 2,500 W. Central air pushes 3,000 to 5,000 W. The BTU/h input method converts cooling capacity to watts, but real AC electrical draw is lower than the raw conversion suggests because the unit moves heat rather than generating it.

 

What is a duty cycle on an appliance?

Duty cycle is the percentage of time an appliance draws full power while switched on. A fridge cycles at about 35%. An AC during cooling season sits around 65%. Continuous loads like a TV or desktop PC run at 100%. Entering the right duty cycle is the difference between an accurate estimate and one that’s three times too high.

 

How do you convert BTU to watts?

Divide BTU per hour by 3.412142. A 12,000 BTU air conditioner equals roughly 3,517 W of cooling capacity. For a heat pump or AC, the electrical draw is typically one-third of that because the unit moves heat rather than creating it. The calculator uses the BTU figure directly for cooling loads.

 

How much does it cost to run a tumble dryer?

A 3,000 W dryer used twice a week for an hour at 90% duty uses about 281 kWh per year. At £0.24/kWh, that’s £67 annually. Heat pump dryers cut the figure to about £22 because they run at 800 to 1,000 W instead of 3,000. The cost gap pays back the higher purchase price within three to four years.

 

What uses the most electricity in a home?

Heating and cooling top the list, followed by water heating, then large appliances like fridges and dryers. In most homes, HVAC accounts for 40% to 50% of the bill. Water heating adds another 15% to 20%. Fridges and freezers sit around 7%. Lighting and electronics make up the remainder. The calculator helps you check any single appliance against these averages.

 

Do appliances use power when switched off?

Yes. Standby power draws 0.5 to 5 W per device in most homes. Across 20 always-on devices, that’s 10 to 100 W continuously, adding 88 to 876 kWh per year. The cost ranges from £21 to £210 depending on your rate. Unplugging unused electronics or using switched power strips eliminates most of this draw.

 

Why does my energy bill not match the calculator?

Standby loads, variable duty cycles, seasonal usage shifts, and tariff structure all sit outside the calculation. The tool models one appliance at one power level over a fixed schedule. Real households mix appliances, weather, and habits in ways that no single-appliance estimate can capture. Use the calculator to compare appliances against each other, not to predict the whole bill.

Disclaimer

This calculator estimates energy use from the inputs you provide. Real consumption varies with appliance age, ambient temperature, load, and how often the unit cycles. Electricity prices change by season and tariff. Carbon intensity depends on your regional grid mix at the time you use the appliance, not just the annual average. Don’t use these figures for billing disputes or equipment sizing. For anything involving electrical installation, consult a licensed electrician. The wattage presets reflect typical modern appliances, not your specific model.

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