Electricity Cost Calculator

What is an electricity cost calculator?

An electricity cost calculator turns three everyday numbers — a device’s power in watts, the hours you run it per day, and your price per kWh — into the cost of running that device per day, per month and per year. It is the fastest way to answer “how much does this appliance actually cost me?” without reading a meter. Homeowners, renters, landlords and small businesses use it to budget bills, compare appliances, decide whether an old fridge or a space heater is worth replacing, and spot the hidden cost of devices left on around the clock.

How the electricity cost calculator works

The calculator uses two steps. First it converts power and time into energy, then it prices that energy:

• Energy per day (kWh) = watts ÷ 1000 × hours used per day. Dividing watts by 1000 converts to kilowatts, and multiplying by daily hours gives kilowatt-hours.
• Daily cost = kWh × price per kWh.
• Monthly cost ≈ daily cost × 30, and yearly cost ≈ daily cost × 365.

The terms and units are:

• Power — how fast the device draws energy, in watts (W). A label may show this directly or as amps and volts (watts = volts × amps).
• Hours used per day — runtime in hours (h), including fractions like 0.5 for 30 minutes.
• Energy — in kilowatt-hours (kWh), the unit utilities bill by.
• Price per kWh — your rate from the bill, in your currency per kWh.

Examples

Each example uses only the formulas above, so you can reproduce every answer by entering the same values into the calculator.

Example 1 — a space heater

A 1,500 W heater run 3 h/day at $0.17/kWh.

kWh/day = 1500 ÷ 1000 × 3 = 1.5 × 3 = 4.5 kWh daily cost = 4.5 × 0.17 = $0.765 monthly ≈ 0.765 × 30 = $22.95 yearly ≈ 0.765 × 365 ≈ $279

The heater costs about $0.765 per day, roughly $22.95 per month and $279 per year.

Example 2 — an LED bulb

A 100 W bulb left on 5 h/day at $0.17/kWh.

kWh/day = 100 ÷ 1000 × 5 = 0.1 × 5 = 0.5 kWh daily cost = 0.5 × 0.17 = $0.085 monthly ≈ 0.085 × 30 = $2.55 yearly ≈ 0.085 × 365 ≈ $31.03

The bulb costs about $0.085 per day, near $2.55 per month and $31 per year.

Example 3 — a refrigerator

A 150 W fridge that effectively runs 24 h/day at $0.17/kWh.

kWh/day = 150 ÷ 1000 × 24 = 0.15 × 24 = 3.6 kWh daily cost = 3.6 × 0.17 = $0.612 monthly ≈ 0.612 × 30 = $18.36 yearly ≈ 0.612 × 365 ≈ $223.38

The fridge costs about $0.612 per day, roughly $18.36 per month and $223 per year.

Appliance running-cost reference

This chart holds the rate at $0.17/kWh and shows the daily, monthly and yearly cost for common devices at typical wattage and runtime. Daily cost is watts ÷ 1000 × hours × rate; monthly is daily × 30; yearly is daily × 365.

Device	Power (W)	Hours/day	kWh/day	Daily	Monthly	Yearly
LED bulb	100	5	0.5	$0.085	$2.55	$31.03
Refrigerator	150	24	3.6	$0.612	$18.36	$223.38
Space heater	1500	3	4.5	$0.765	$22.95	$279.23
Window AC	1000	8	8.0	$1.36	$40.80	$496.40
Desktop PC	200	6	1.2	$0.204	$6.12	$74.46

Notice how a small wattage running 24 hours (the fridge) can outcost a large wattage used briefly — runtime matters as much as power.

Common uses

• Budgeting a bill — adding up the per-month cost of your biggest devices to see where the money goes.
• Comparing appliances — checking the yearly cost of an old fridge or dryer against a newer, lower-wattage model before buying.
• Justifying upgrades — seeing whether the yearly saving from an efficient device pays back its purchase price.
• Renters and shared homes — splitting or estimating costs for heaters, AC units and other heavy loads.
• Phantom loads — pricing devices left on standby or running around the clock, where small wattages add up over 365 days.

Tips and common mistakes

• Use your own rate. The default examples use $0.17/kWh, but prices vary widely by region, plan and time of day. Copy the exact price per kWh from your bill for an accurate result.
• Convert amps to watts first. If a label shows volts and amps, multiply them: a 120 V, 5 A device draws 600 W. Entering 5 instead of 600 understates the cost by a huge margin.
• Count real runtime, not “always plugged in.” A heater with a thermostat or a fridge with a compressor cycles on and off; estimate the hours it is actually drawing power.
• Watch kilowatts versus watts. A “1.5 kW” heater is 1,500 W. Forgetting to multiply by 1000 makes the cost 1000 times too small.
• Treat 30 and 365 as estimates. Monthly cost uses a flat 30 days and yearly uses 365, so a 31-day month or seasonal use will differ slightly.

Limitations and notes

This calculator gives a clean estimate using a single, steady wattage and a flat price per kWh. Real bills can differ because many appliances cycle or vary their draw (fridges, AC units, washers heating water), because tiered or time-of-use tariffs charge different rates at different times, and because fixed daily standing charges and taxes are added on top of usage. The monthly and yearly figures assume identical usage every day via the × 30 and × 365 multipliers, which is only an approximation. The arithmetic is exact for the numbers you type, so accuracy depends on using your real wattage, runtime and rate. The tool runs entirely in your browser — your inputs stay on your device and nothing is uploaded or stored.

For related calculations, try the kinetic energy calculator for the energy of moving objects, the Ohm’s law calculator to work out volts, amps, ohms and watts, or the combined gas law calculator for pressure, volume and temperature — and browse more in the chemistry and physics category.