# 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.

- Calculator id: `electricity-cost` · Category: Everyday Life (`everyday`) · Tool name: `calculate_electricity_cost`
- Canonical page: https://tttkmbb.com/everyday/electricity-cost · This document: https://tttkmbb.com/everyday/electricity-cost.md · JSON definition: https://tttkmbb.com/everyday/electricity-cost.json

## Purpose

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.

**Use when:** 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).

## Input

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

## Output

| Field | 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. |

## 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.

## Data Sources

- US DOE – Estimating Appliance and Home Electronic Energy Use — https://www.energy.gov/energysaver/estimating-appliance-and-home-electronic-energy-use (government, retrieved 2026-09-23)

Data freshness: `static`. Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output.

## API

- `GET https://tttkmbb.com/api/v1/calculate/electricity-cost?power_watts=…&hours_per_day=…&price_per_kwh=…`
- `POST https://tttkmbb.com/api/v1/calculate/electricity-cost` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/electricity-cost · OpenAPI operationId `calculate_electricity_cost` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool:  `run_calculator` with `{"calculator_id": "electricity-cost", "inputs": {…}}`

## Example

- 100 W for 5 h/day at 0.15/kWh, 30 days: inputs `{"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: inputs `{"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
```

## Limitations

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). 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. All values are computed from the formula above; no measurement or live data is involved.

## 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

- [Electric Power Calculator](https://tttkmbb.com/physics/electric-power.md) — Compute watts from volts and amps or resistance.
- [Energy Converter](https://tttkmbb.com/conversion/energy.md) — Convert kWh to joules, BTU or calories.