# Boiling Point at Altitude Calculator

> Computes the boiling point of water at a given altitude by taking the ISA pressure at that altitude (or a measured station pressure) and solving the Antoine equation for water, with a note on cooking at altitude.

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

## Purpose

Computes the boiling point of water at a given altitude by taking the ISA pressure at that altitude (or a measured station pressure) and solving the Antoine equation for water, with a note on cooking at altitude.

**Use when:** You need the boiling temperature of water at your elevation for cooking, canning, brewing, candy making or laboratory work, or the boiling point at a measured barometric pressure.

**Do not use when:** You need the boiling point of a liquid other than water or of salt/sugar solutions (boiling-point elevation), or altitudes above 9000 m.

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `altitude` | number |  | required | Elevation above sea level in altitude_unit (−500 to 9000 m). (min -1640, max 29500) |
| `altitude_unit` | enum: m \| ft |  | optional, default "m" | Unit of the altitude input. |
| `pressure_hpa` | number | hPa | optional | Actual absolute pressure at the site in hPa; when given it replaces the standard-atmosphere pressure for the altitude. (min 200, max 1100) |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `boiling_point_c` | number | °C | Boiling temperature of pure water at the site pressure. |
| `boiling_point_f` | number | °F | Boiling point in Fahrenheit. |
| `boiling_point_drop_c` | number | °C | 100 °C minus the local boiling point. |
| `pressure_hpa` | number | hPa | Standard-atmosphere pressure at the altitude, or the measured pressure if supplied. |
| `pressure_mmhg` | number | mmHg | Same pressure in millimetres of mercury. |
| `altitude_m` | number | m | Altitude in metres. |
| `altitude_ft` | number | ft | Altitude in feet. |
| `cooking_note` | string |  | Practical consequence for boiling and simmering food at this altitude. |

## Formula

`p = 1013.25 × (1 − 0.0065·h/288.15)^5.25578 hPa (ISA); P_mmHg = p / 1.333224; T_boil = 1730.63 / (8.07131 − log10(P_mmHg)) − 233.426 °C (Antoine equation for water, valid 1–100 °C)`

The standard atmosphere is an average; on a given day the real pressure, and hence the boiling point, varies by about ±0.5 °C with weather. Rule of thumb: the boiling point falls about 1 °C per 300 m (1 °F per 500 ft).

## Data Sources

- Wikipedia – Antoine equation (water coefficients, 1–100 °C) — https://en.wikipedia.org/wiki/Antoine_equation (reference, retrieved 2026-09-24)
- Wikipedia – International Standard Atmosphere (ICAO Doc 7488) — https://en.wikipedia.org/wiki/International_Standard_Atmosphere (reference, retrieved 2026-09-24)
- Wikipedia – High-altitude cooking (boiling point table) — https://en.wikipedia.org/wiki/High-altitude_cooking (reference, 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/boiling-point-altitude?altitude=…`
- `POST https://tttkmbb.com/api/v1/calculate/boiling-point-altitude` 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/boiling-point-altitude · OpenAPI operationId `calculate_boiling_point_at_altitude` 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": "boiling-point-altitude", "inputs": {…}}`

## Example

- 1500 m: inputs `{"altitude":1500,"altitude_unit":"m"}` → `{"boiling_point_c":95,"boiling_point_f":203,"boiling_point_drop_c":5,"pressure_hpa":845.6,"pressure_mmhg":634.2,"altitude_ft":4921}`
- Denver, 5280 ft: inputs `{"altitude":5280,"altitude_unit":"ft"}` → `{"boiling_point_c":94.7,"boiling_point_f":202.4,"altitude_m":1609,"pressure_hpa":834.3}`

```
GET https://tttkmbb.com/api/v1/calculate/boiling-point-altitude?altitude=1500&altitude_unit=m
```

## Limitations

You need the boiling point of a liquid other than water or of salt/sugar solutions (boiling-point elevation), or altitudes above 9000 m. The standard atmosphere is an average; on a given day the real pressure, and hence the boiling point, varies by about ±0.5 °C with weather. Rule of thumb: the boiling point falls about 1 °C per 300 m (1 °F per 500 ft). All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**Why does food take longer to cook at altitude?**

Boiling water is cooler, so heat transfers into the food more slowly; pasta, rice, beans and eggs need more time and often more liquid, and some foods never soften without a pressure cooker.

**Does adding salt raise the boiling point noticeably?**

Barely: a typical 1 % kitchen brine raises it by about 0.2 °C, far less than the drop from a few hundred metres of elevation.

**Which pressure should I enter?**

The absolute (station) pressure read at the site, not the sea-level-corrected value from weather reports; leave it empty to use the standard atmosphere.

## Related

- [Pressure Altitude Calculator](https://tttkmbb.com/weather/pressure-altitude.md) — Standard pressure at an altitude and station pressure from QNH.
- [Turkey Cooking Time Calculator](https://tttkmbb.com/food/turkey-cooking-time.md) — Roasting times also change with altitude and oven temperature.
- [Temperature Converter](https://tttkmbb.com/conversion/temperature.md) — Convert the boiling point between °C and °F.