Temperature at altitude calculator
If it is 20 °C at sea level, expect about 10.25 °C at 1,500 m, since the standard atmosphere loses 6.5 °C every 1,000 m. Enter the sea-level temperature and an altitude to get the air temperature there in Celsius and Fahrenheit. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Altitude
- 1,500
- Sea level temp
- 20
- Altitude m
- 1,500 c
- Sea level temp c
- 20
- Lapse rate c per m
- 0.0065
- Temperature c
- 10.25
The altitude temperature calculator estimates how cold the air gets as you climb. Give it the temperature at sea level and an altitude in metres, and it applies the standard atmospheric lapse rate — about 6.5 °C lost for every 1000 metres gained — to return the expected temperature at that height, in Celsius or Fahrenheit. It is the same rule of thumb pilots, hikers and weather forecasters use, computed deterministically in a single call, with both temperature units always included in the response.
What the lapse rate is and why it matters
Air cools as it rises because pressure drops with altitude and expanding air does work, losing heat. The International Standard Atmosphere models this cooling in the troposphere as a constant lapse rate of 6.5 °C per 1000 metres (0.0065 °C per metre), which holds reasonably well from sea level up to about 11 000 metres.
This temperature at altitude calculator applies that linear model to your own starting point: you supply the temperature at sea level — a measurement from a nearby station, a forecast, or the current reading outside — and the tool subtracts 6.5 °C for each kilometre of altitude. The result is the expected free-air temperature at that height under standard conditions. It matters because the difference is large: a pleasant 20 °C day at the coast becomes about 5 °C at 2300 metres, roughly the elevation of many mountain passes.
Knowing the expected temperature before you climb decides what clothing, fuel and water you carry, and it is the first number in any mountain weather assessment.
How the computation works
The formula is deliberately simple: T(h) = T0 − L·h, where T0 is your sea-level temperature in Celsius, L is the standard lapse rate of 0.0065 °C per metre, and h is the altitude in metres. The response always reports the result in both Celsius and Fahrenheit (using the exact conversion °F = °C·9/5 + 32) and echoes the altitude and the sea-level temperature you supplied, so the output is self-documenting and easy to log.
Negative altitudes are accepted: below sea level, in places such as Death Valley or the Dead Sea basin, the air is warmer than your sea-level reference, and the formula reflects that by adding heat back at the same rate.
Limitations and honest use
A linear lapse rate is an average, not a forecast. Real atmospheres deviate from the standard model: a temperature inversion can make a valley colder than the ridge above it, a dry air mass cools at close to 9.8 °C per 1000 metres while saturated air cools more slowly, and weather systems routinely override the climatological mean by ten degrees or more. Treat the result as the expected temperature in a standard atmosphere and check an actual mountain forecast before decisions where safety depends on it.
Used honestly, though, the estimate is remarkably useful: it calibrates intuition, it is the right first guess when no better data exists, and it is exactly the model used in aviation for standard-atmosphere calculations. No measurement is stored, and nothing leaves the deterministic arithmetic described here.
What you can do with it
Plan a mountain hike
Convert the forecast for the valley town into the temperature you should expect at the summit, and pack layers for the real number.
Pre-flight and drone planning
Estimate outside air temperature at cruising or operating altitude from a sea-level observation for performance and battery calculations.
Teaching atmospheric physics
Demonstrate the lapse rate with concrete numbers: students change altitude and see the linear cooling immediately, in °C or °F.
FAQ
What lapse rate does it use?
The International Standard Atmosphere value for the troposphere: 6.5 °C per 1000 metres (0.0065 °C/m), applied to your own sea-level temperature.
What happens if the altitude is not a number?
NaN, Infinity and non-numeric text are rejected rather than producing a meaningless result.
Are negative altitudes supported?
Yes. Below sea level the formula returns a temperature warmer than the sea-level value, at the same 6.5 °C per 1000 m rate.
How accurate is the estimate?
It is the standard-atmosphere expectation, good to a few degrees in typical conditions. Inversions, humidity and weather systems can shift real temperatures far from it — use a mountain forecast when precision matters.
How cold will it be at 2,300 metres if it is 20 °C at the coast?
About 5 °C under the standard lapse rate, roughly the height of many mountain passes. Knowing that before you climb helps decide the clothing, fuel and water you carry.
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/phys/altitude-temperature \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"altitude":1500,"sea_level_temp":20}'const res = await fetch("https://api.kit.forhosting.com/phys/altitude-temperature", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"altitude": 1500,
"sea_level_temp": 20
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/phys/altitude-temperature",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"altitude": 1500,
"sea_level_temp": 20
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/phys/altitude-temperature", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"altitude":1500,"sea_level_temp":20}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"altitude":1500,"sea_level_temp":20}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/phys/altitude-temperature", 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": 1500,
"sea_level_temp": 20
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "phys.altitude_temperature",
"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.
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
How the computation works
Because the model is linear, the endpoint is deterministic — the same input always produces exactly the same output, with no sampling, no network lookups and no hidden assumptions. The altitude must be a finite number — NaN or Infinity raises an invalid_input error rather than silently returning nonsense, and non-numeric text is rejected for the same reason.
Limitations and honest use
The tool runs free in your browser on this page with the same code that serves the API, so you can verify any result by hand, and you only pay — $0.002 per request — when you automate calls against the API.
Technical questions
What does it cost?
$0.002 per request via the API. It is also free to run in your browser on this page with the same code.
Can I get the result in Fahrenheit?
Yes. Pass unit 'f' for the main result in Fahrenheit; the response always includes both temperature_c and temperature_f regardless.