Home › Everyday Life › Electricity Cost Calculator

Electricity Cost Calculator

Converts an appliance's power draw and daily usage into kilowatt-hours and the running cost per day, over a chosen number of days, per 30-day month and per 365-day year, using the US DOE energy-use formula.

When to use

You want to know what a heater, fridge, computer, light or EV charger costs to run, or compare two appliances by energy cost.

Do not use when: The appliance cycles or has standby modes with unknown duty cycle (use a measured kWh figure or plug-in meter), or you need to convert energy units (use energy).

Formula

kWh/day = power_watts × hours_per_day / 1000; cost/day = kWh/day × price_per_kwh; period = × days; month = × 30; year = × 365

Assumes constant power while running. Appliances with thermostats or motors (fridges, heaters, pumps) run only part of the time, so use their measured average draw or reduce hours_per_day accordingly.

Inputs

Parameter	Type	Unit	Required	Description
`power_watts`	number	W	yes	Power draw in watts while running (1 kW = 1000 W). Range: > 0, ≤ 1000000
`hours_per_day`	number	h/day	yes	Hours the appliance actually draws that power each day. Range: ≥ 0, ≤ 24
`price_per_kwh`	number	per kWh	yes	Tariff per kilowatt-hour in your currency (from your bill). Range: ≥ 0, ≤ 100
`days`	integer	days	default 30	Length of the billing period to report. Range: ≥ 1, ≤ 3660

Outputs

Output	Type	Unit	Description
`kwh_per_day`	number	kWh/day	power_watts × hours_per_day / 1000.
`cost_per_day`	number		kwh_per_day × price_per_kwh.
`kwh_for_period`	number	kWh	kwh_per_day × days.
`cost_for_period`	number		cost_per_day × days.
`cost_per_month`	number		cost_per_day × 30.
`cost_per_year`	number		cost_per_day × 365.

Example

100 W for 5 h/day at 0.15/kWh, 30 days: {"power_watts":100,"hours_per_day":5,"price_per_kwh":0.15,"days":30} → {"kwh_per_day":0.5,"cost_per_day":0.075,"kwh_for_period":15,"cost_for_period":2.25,"cost_per_month":2.25,"cost_per_year":27.38}

1500 W heater 8 h/day at 0.30/kWh, 90 days: {"power_watts":1500,"hours_per_day":8,"price_per_kwh":0.3,"days":90} → {"kwh_per_day":12,"cost_per_day":3.6,"kwh_for_period":1080,"cost_for_period":324,"cost_per_month":108,"cost_per_year":1314}

GET https://tttkmbb.com/api/v1/calculate/electricity-cost?power_watts=100&hours_per_day=5&price_per_kwh=0.15&days=30

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/electricity-cost (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/electricity-cost · Markdown: https://tttkmbb.com/everyday/electricity-cost.md · JSON definition: https://tttkmbb.com/everyday/electricity-cost.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="electricity-cost"
OpenAPI operationId: calculate_electricity_cost
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

US DOE – Estimating Appliance and Home Electronic Energy Use (government)

FAQ

Where do I find the wattage?

On the appliance label or in its manual; if only amps are given, watts = volts × amps (e.g. 230 V × 0.5 A = 115 W). A plug-in power meter gives the real average draw.

Does the price include taxes and standing charges?

Use the all-in price per kWh from your bill (energy price plus per-kWh levies); fixed daily standing charges are not per-kWh and are not included.

Related calculators

Electric Power Calculator — Compute watts from volts and amps or resistance.
Energy Converter — Convert kWh to joules, BTU or calories.