Boiling point altitude calculator
At sea level pure water boils at 100 °C (373.15 K, 212 °F), and thinner air at altitude lowers that point. Enter your elevation or your absolute barometer reading to adjust boil times, candy stages or a chemistry answer. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Altitude
- 0
- Calculation mode
- altitude
- Boiling point c
- 100
- Boiling point k
- 373.15
- Boiling point f
- 212
This boiling point altitude calculator estimates the temperature at which pure water boils when you know either the elevation above sea level or the absolute atmospheric pressure. At sea level the familiar normal boiling point is about one hundred degrees Celsius, but thinner air at altitude lowers the saturation vapor pressure match, so water simmers sooner—an effect cooks notice in high cities and hikers see on mountain stoves. The engine first obtains absolute pressure from the International Standard Atmosphere troposphere formula when you supply altitude, or converts your pressure reading into pascals when you already know the local barometer. It then applies the integrated Clausius–Clapeyron relation with a constant latent heat of vaporization to map that pressure onto an approximate boiling temperature in Celsius, kelvin, and Fahrenheit. Negative absolute pressure is rejected as invalid, because it has no physical meaning for this model. The arithmetic is fully deterministic with no network weather feeds, no sampling, and no date-dependent shortcuts.
What boiling point versus altitude means and what you get
Pure water boils when its vapor pressure equals the surrounding absolute atmospheric pressure. At the standard one-atmosphere reference that equality sits near three hundred seventy-three point one five kelvin, or one hundred degrees Celsius. Raise elevation in the troposphere and the standard atmosphere model predicts a lower pressure; the Clausius–Clapeyron slope then maps that lower pressure onto a lower saturation temperature, which is why recipes from sea-level kitchens undercook pasta if you ignore elevation.
When altitude is the input it also echoes altitude in meters and the original unit; when pressure is the input it echoes the raw reading and unit.
Where boiling-point altitude checks fit in study, cooking, and software
Students meet boiling-point depression with altitude when a chemistry unit links vapor pressure to the phase diagram, when a geography or outdoor-education lesson asks why water boils cooler on a mountain, or when a physics homework set supplies either elevation or barometer readings and demands Celsius and kelvin answers. Teachers can pre-generate answer keys for modest elevations without trusting opaque apps that silently switch feet and meters or forget absolute versus gauge pressure.
Cooks and bakers use the same numbers when adapting boil times, candy stages, or canning guidance for high cities, while backpackers estimate stove performance before a trek. Developers call the contract from scripts to seed deterministic test vectors for thermo demos, to normalize user-entered elevation into a boiling temperature for recipe apps, or to satisfy programming-challenge statements that demand a reproducible Tb rather than a hand-waved rule of one degree per three hundred meters.
What you can do with it
Homework and lab checks
Estimate pure-water boiling temperature from elevation or absolute pressure for chemistry, physics, and outdoor-education worksheets.
High-altitude cooking and field planning
Convert city elevation or barometer readings into approximate Tb for recipe timing, canning caution, and stove expectations.
FAQ
What does the boiling point altitude calculator cost?
It is free in your browser on this page.
Do I enter altitude or pressure?
Exactly one of them. Altitude uses the ISA troposphere barometric formula then Clausius–Clapeyron; pressure skips the ISA step and uses Clausius–Clapeyron directly.
What happens if pressure is negative?
Absolute atmospheric pressure cannot be negative in this boiling-point model.
Why is sea-level boiling not always exactly 100 °C in the output?
The Clausius–Clapeyron constants are an engineering approximation with fixed latent heat. At the reference pressure of 101325 Pa the result is extremely close to 100 °C; floating-point rounding at your chosen precision may show tiny residuals.
Which altitude and pressure units are supported?
Altitude defaults to meters and also accepts feet. Pressure defaults to pascals and accepts kPa, hPa, mbar, bar, atm, mmHg, torr, and psi.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/thermo/boiling-point-altitude \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"altitude":0,"h":1}'const res = await fetch("https://api.kit.forhosting.com/thermo/boiling-point-altitude", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"altitude": 0,
"h": 1
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/thermo/boiling-point-altitude",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"altitude": 0,
"h": 1
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/thermo/boiling-point-altitude", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"altitude":0,"h":1}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"altitude":0,"h":1}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/thermo/boiling-point-altitude", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"altitude": 0,
"h": 1
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "thermo.boiling_point_altitude",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Limits
max_abs_altitude_m | 11000 |
max_abs_pressure_pa | 1000000000000000 |
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
What boiling point versus altitude means and what the response contains
This calculator returns the mode tag altitude or pressure, boiling_point_c, boiling_point_k, and boiling_point_f, the absolute pressure used in pascals and atmospheres, the precision applied, a method tag clausius_clapeyron_isa, and a short formula reminder. There is no real-time METAR download, no humidity correction, and no solute depression model: the engine either evaluates the closed-form ISA-plus-Clausius–Clapeyron path inside the supported ranges or rejects the request with invalid_input. Rejected cases include missing both altitude and pressure, supplying both at once, non-finite numbers, altitude outside the documented troposphere window, non-positive pressure, and explicitly negative pressure, which is called out because absolute barometer readings cannot go negative in this physics.
How altitude and pressure are read and how Tb stays reproducible
You must provide exactly one of the two: the altitude path runs the ISA barometric formula first, while the pressure path skips straight to Clausius–Clapeyron. Optional leading plus signs and scientific notation on numeric strings are allowed when they parse as finite decimals; embedded spaces and non-numeric tokens are rejected with a clear message so a bad cell does not become a wrong boiling point. Altitude is limited to roughly negative five hundred meters through eleven thousand meters so the troposphere temperature-ratio form stays positive. Preferred fields are altitude for elevation and pressure for absolute atmospheric pressure, with aliases such as h, elevation, and elev for height, and P, p, and atm_pressure for pressure, so spreadsheets, query strings, and typed forms can reuse the same contract. Optional altitude_unit accepts m or ft and defaults to meters; optional pressure_unit accepts Pa, kPa, hPa, mbar, bar, atm, mmHg, torr, or psi and defaults to pascals. Negative pressure fails immediately with invalid_input and a message that absolute atmospheric pressure cannot be negative for a boiling-point calculation; zero or near-zero pressure is likewise rejected because the logarithm in Clausius–Clapeyron is undefined or extreme. An optional precision field, with aliases decimals and dp, chooses how many decimal places to expose, defaulting to ten and capped at fifteen so JSON goldens stay stable. Pair the free browser run on this page with the priced API when you need the identical mathematical result inside an automated pipeline without re-implementing ISA and Clausius–Clapeyron yourself.
Where boiling-point altitude checks fit in study, cooking, and software
Product and education tools use the endpoint when a learner types an altitude or a pressure and the UI must show Celsius, kelvin, Fahrenheit, and the absolute pressure assumed. On this page the work runs entirely in your browser; through the API each successful lookup costs $0.002, failed validation is not charged, and nothing is stored after the response returns. That split—free interactive exploration and a priced, identical API—matches the rest of the KIT tier-A catalog and lets you move from a classroom demo to an automated pipeline without changing the mathematical result. Pair it with other thermo helpers when you need latent heat or gas-law steps, and with math endpoints when you are building a small lab of free, deterministic physics calculators.
Integration use cases
Deterministic test fixtures
Generate reproducible boiling-point results for unit tests, thermo demos, and CI assertions without network weather data.