# Electric Power Calculator

> Computes electrical power from voltage and current (or the current drawn by a known power at a given voltage), the equivalent resistance, and, with hours of use and a tariff, the energy in kWh and its cost.

- Calculator id: `electric-power` · Category: Physics (`physics`) · Tool name: `calculate_electric_power`
- Canonical page: https://tttkmbb.com/physics/electric-power · This document: https://tttkmbb.com/physics/electric-power.md · JSON definition: https://tttkmbb.com/physics/electric-power.json

## Purpose

Computes electrical power from voltage and current (or the current drawn by a known power at a given voltage), the equivalent resistance, and, with hours of use and a tariff, the energy in kWh and its cost.

**Use when:** You need the wattage or amperage of an appliance, whether it fits a circuit rating, or how much energy and money it uses over a period.

**Do not use when:** The load has a power factor below 1 (motors, some electronics: P = V·I·cos φ), you only need V, I and R relations (use ohms-law), or you want a multi-appliance bill (use electricity-cost).

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `voltage_v` | number | V | required | Supply voltage in volts (e.g. 230 in Europe, 120 in North America, 12 for automotive). (> 0) |
| `current_a` | number | A | optional | Current drawn in amperes. Give either current_a or power_w. (min 0) |
| `power_w` | number | W | optional | Rated power in watts. Give either current_a or power_w. (min 0) |
| `usage_hours` | number | h | optional | Optional operating time; enables the energy output. (min 0) |
| `price_per_kwh` | number | per kWh | optional | Optional tariff in your currency per kilowatt-hour; enables the cost output. (min 0) |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `power_w` | number | W | P = V × I. |
| `power_kw` | number | kW | Power in kilowatts. |
| `current_a` | number | A | I = P / V. |
| `resistance_ohm` | number | Ω | R = V / I for a purely resistive load. |
| `energy_kwh` | number | kWh | P × usage_hours / 1000 (only when usage_hours is given). |
| `energy_cost` | number |  | energy_kwh × price_per_kwh (only when usage_hours and price_per_kwh are given). |

## Formula

`power_w = voltage_v × current_a (or current_a = power_w / voltage_v); resistance_ohm = voltage_v / current_a; energy_kwh = power_w × usage_hours / 1000; energy_cost = energy_kwh × price_per_kwh`

## Data Sources

- HyperPhysics – Electric power — http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elepow.html (reference, retrieved 2026-09-23)
- Wikipedia – Electric power — https://en.wikipedia.org/wiki/Electric_power (reference, 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/electric-power?voltage_v=…`
- `POST https://tttkmbb.com/api/v1/calculate/electric-power` 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/electric-power · OpenAPI operationId `calculate_electric_power` 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": "electric-power", "inputs": {…}}`

## Example

- 230 V, 6.5 A for 2 h at 0.30 per kWh: inputs `{"voltage_v":230,"current_a":6.5,"usage_hours":2,"price_per_kwh":0.3}` → `{"power_w":1495,"power_kw":1.495,"current_a":6.5,"resistance_ohm":35.3846,"energy_kwh":2.99,"energy_cost":0.9}`
- 1500 W heater on 120 V: inputs `{"voltage_v":120,"power_w":1500}` → `{"power_w":1500,"current_a":12.5,"resistance_ohm":9.6}`

```
GET https://tttkmbb.com/api/v1/calculate/electric-power?voltage_v=230&current_a=6.5&usage_hours=2&price_per_kwh=0.3
```

## Limitations

The load has a power factor below 1 (motors, some electronics: P = V·I·cos φ), you only need V, I and R relations (use ohms-law), or you want a multi-appliance bill (use electricity-cost). All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**Is the nameplate wattage the actual consumption?**

It is the maximum rating. Thermostat-controlled appliances (heaters, fridges) draw it only part of the time, so real energy use is lower.

**What about three-phase or AC loads?**

For single-phase AC the formula gives apparent power (VA); real power is V·I·cos φ. Three-phase power is √3 × V_line × I × cos φ and is not covered here.

## Related

- [Ohm's Law Calculator](https://tttkmbb.com/physics/ohms-law.md) — Voltage, current and resistance relations.
- [Electricity Cost Calculator](https://tttkmbb.com/everyday/electricity-cost.md) — Running cost of several appliances over a period.
- [Work & Power Calculator](https://tttkmbb.com/physics/work-power.md) — Mechanical power from work and time.