# Wind Chill Calculator

> Computes the wind chill temperature from air temperature and wind speed with the 2001 JAG/TI formula used by the US National Weather Service and Environment Canada, and reports the frostbite risk band for exposed skin.

- Calculator id: `wind-chill` · Category: Weather & Environment (`weather`) · Tool name: `calculate_wind_chill`
- Canonical page: https://tttkmbb.com/weather/wind-chill · This document: https://tttkmbb.com/weather/wind-chill.md · JSON definition: https://tttkmbb.com/weather/wind-chill.json

## Purpose

Computes the wind chill temperature from air temperature and wind speed with the 2001 JAG/TI formula used by the US National Weather Service and Environment Canada, and reports the frostbite risk band for exposed skin.

**Use when:** You need the 'feels like' temperature in cold windy weather, or how quickly exposed skin can freeze, for temperatures at or below 10 °C (50 °F) and winds of at least 4.8 km/h (3 mph).

**Do not use when:** The temperature is above 10 °C (50 °F) or the wind is below 4.8 km/h (the formula is undefined there); for hot humid weather use heat-index.

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `temperature` | number |  | required | Air temperature in temperature_unit; must be at or below 10 °C (50 °F). (min -100, max 60) |
| `temperature_unit` | enum: c \| f |  | optional, default "c" | Unit of the temperature input(s). |
| `wind_speed` | number |  | required | Wind speed measured at 10 m (standard anemometer height), in wind_speed_unit; must be at least 4.8 km/h (3 mph). (min 0, max 400) |
| `wind_speed_unit` | enum: kmh \| mph \| ms \| knots |  | optional, default "kmh" | Unit of the wind speed input. |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `wind_chill_c` | number | °C | Wind chill temperature in Celsius. |
| `wind_chill_f` | number | °F | Wind chill temperature in Fahrenheit. |
| `temperature_c` | number | °C | Input temperature in Celsius. |
| `wind_speed_kmh` | number | km/h | Input wind speed in km/h. |
| `frostbite_risk` | string |  | Environment Canada risk band for the wind chill value. |
| `frostbite_time` | string |  | Freezing time for exposed skin from the Environment Canada table (bands start at −28 °C). |

## Formula

`WC(°C) = 13.12 + 0.6215·T − 11.37·V^0.16 + 0.3965·T·V^0.16 with T in °C and V in km/h (identical to the NWS form WC(°F) = 35.74 + 0.6215·T − 35.75·V^0.16 + 0.4275·T·V^0.16 with T in °F, V in mph); defined for T ≤ 10 °C and V ≥ 4.8 km/h`

The 2001 Joint Action Group for Temperature Indices formula models heat loss from a bare face walking at 4.8 km/h into the wind, with wind measured at 10 m. Frostbite bands: −28 to −39 °C skin freezes in 10–30 min, −40 to −47 in 5–10 min, −48 to −54 in 2–5 min, −55 and colder in under 2 min.

## Data Sources

- NWS – Wind Chill Chart (2001 JAG/TI formula) — https://www.weather.gov/safety/cold-wind-chill-chart (government, retrieved 2026-09-24)
- Environment and Climate Change Canada – Wind chill and the Wind Chill Index (frostbite risk table) — https://www.canada.ca/en/services/environment/weather/severeweather/wind-chill-index.html (government, retrieved 2026-09-24)

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/wind-chill?temperature=…&wind_speed=…`
- `POST https://tttkmbb.com/api/v1/calculate/wind-chill` 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/wind-chill · OpenAPI operationId `calculate_wind_chill` 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": "wind-chill", "inputs": {…}}`

## Example

- −10 °C, 30 km/h: inputs `{"temperature":-10,"temperature_unit":"c","wind_speed":30,"wind_speed_unit":"kmh"}` → `{"wind_chill_c":-19.5,"wind_chill_f":-3.1,"wind_speed_kmh":30,"frostbite_risk":"Moderate risk (−10 to −27 °C)"}`
- 5 °F, 25 mph: inputs `{"temperature":5,"temperature_unit":"f","wind_speed":25,"wind_speed_unit":"mph"}` → `{"wind_chill_f":-17.5,"wind_chill_c":-27.5,"temperature_c":-15,"wind_speed_kmh":40.2}`

```
GET https://tttkmbb.com/api/v1/calculate/wind-chill?temperature=-10&temperature_unit=c&wind_speed=30&wind_speed_unit=kmh
```

## Limitations

The temperature is above 10 °C (50 °F) or the wind is below 4.8 km/h (the formula is undefined there); for hot humid weather use heat-index. The 2001 Joint Action Group for Temperature Indices formula models heat loss from a bare face walking at 4.8 km/h into the wind, with wind measured at 10 m. Frostbite bands: −28 to −39 °C skin freezes in 10–30 min, −40 to −47 in 5–10 min, −48 to −54 in 2–5 min, −55 and colder in under 2 min. All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**Why is there no result for light winds or mild temperatures?**

The formula is only defined for air temperatures at or below 10 °C (50 °F) and winds of at least 4.8 km/h (3 mph); outside that range the calculator returns an error rather than a misleading number.

**Is the wind measured at face height?**

No. The formula expects the standard 10 m anemometer wind; it internally converts to face-level wind (about 2/3 of the 10 m value).

**Does wind chill lower the temperature of objects?**

No. It expresses the rate of heat loss from skin; a car radiator or pipe never cools below the actual air temperature.

## Related

- [Heat Index Calculator](https://tttkmbb.com/weather/heat-index.md) — The hot-weather counterpart.
- [Speed Converter](https://tttkmbb.com/conversion/speed.md) — Convert wind speeds between km/h, mph, m/s and knots.
- [Temperature Converter](https://tttkmbb.com/conversion/temperature.md) — Plain °C ↔ °F conversion.