Convert barometric pressure units
Standard sea-level pressure of 1013.25 hPa is also 1013.25 mb, about 29.921 inHg and 760 mmHg. Enter a reading in any of the four units and see all four at once. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Value
- 1,013.25 hPa
- Hpa
- 1,013.25 hPa
- Mb
- 1,013.25
- Inhg
- 29.9212524019
- Mmhg
- 760
Weather reports, aviation METAR remarks, and home barometers rarely speak the same pressure language. A station in Europe may publish 1013.25 hPa while a US forecast quotes 29.92 inHg and a laboratory log still records millimetres of mercury. This barometric pressure converter accepts a positive magnitude in hectopascals, millibars, inches of mercury, or millimetres of mercury and returns the same reading expressed in all four units using fixed meteorological factors. Millibars match hectopascals one-to-one, so switching between SI weather maps and older mb tables never introduces rounding noise beyond stable display precision.
Barometric units and the hPa conversion bridge
Meteorological surface pressure is almost always reported as a reduced station or sea-level value in one of four practical units: hectopascal (hPa), millibar (mb), inch of mercury (inHg), and millimetre of mercury (mmHg). By World Meteorological Organization practice, one hectopascal equals one millibar exactly, so any map labelled in mb is numerically identical when relabelled in hPa. Inches of mercury remain the default on many North American altimeter and household barometer dials; the conventional factor used here is one inHg equals 33.86389 hPa, matching common aviation and NWS tables.
Millimetres of mercury (treated as torr for this calculator) convert through the exact standard-atmosphere ratio: one mmHg equals 101325 divided by 760 pascals, which is then divided by 100 to land in hPa. The algorithm always bridges through hPa: the input is scaled into hectopascals first, then that intermediate value is divided by the same factors to produce inHg and mmHg, while mb is copied from hPa.
Standard sea-level pressure 1013.25 hPa therefore becomes about 29.921 inHg and 760 mmHg within rounding, which is the familiar triple used in textbooks and altimeter training.
Where a barometric pressure converter earns its keep
Pilots and flight-planning tools convert between inHg altimeter settings and hPa QNH figures when crossing regions that publish different scales, catching transcription errors before they reach a briefing strip. Science educators and exam generators need an oracle that rejects non-positive pressures instead of inventing a silent zero reading that a buggy grader might treat as success. Failed validation does not consume balance.
Use it for METAR study sheets, station log normalisers, and product landing pages that need a trustworthy hPa–inHg–mmHg table without standing up custom conversion code of your own.
What you can do with it
Aviation QNH and altimeter settings
Convert between hPa QNH figures and inHg altimeter settings when briefing flights that cross regions using different pressure scales.
Home weather station dashboards
Normalise sensor readings reported in mb into hPa or inHg for multi-unit household dashboards and automation rules.
Classroom and exam barometer labs
Give students a deterministic hPa–inHg–mmHg oracle that rejects non-positive pressures and matches textbook standard atmosphere checks.
FAQ
Which barometric units can I convert?
Send a positive value with unit hPa, mb, inHg, or mmHg. The response always returns all four: hpa, mb, inhg, and mmhg.
Are hPa and mb the same?
Yes. One hectopascal equals one millibar exactly, so the converter copies hPa to mb without an extra scale factor.
What happens if the pressure value is zero or negative?
Ambient barometric pressure must be strictly positive; invalid values are not billed.
Which conversion factors does the calculator use?
All paths bridge through hPa for stable, deterministic results.
Can I use it to convert altimeter settings?
Yes. It converts between inHg altimeter settings and hPa QNH figures, which helps when a flight crosses regions that publish different pressure scales. Inches of mercury use the common aviation factor of 33.86389 hPa each.
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/weather/barometric-pressure-convert \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"value":1013.25,"unit":"hPa"}'const res = await fetch("https://api.kit.forhosting.com/weather/barometric-pressure-convert", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"value": 1013.25,
"unit": "hPa"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/weather/barometric-pressure-convert",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"value": 1013.25,
"unit": "hPa"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/weather/barometric-pressure-convert", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"value":1013.25,"unit":"hPa"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"value":1013.25,"unit":"hPa"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/weather/barometric-pressure-convert", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"value": 1013.25,
"unit": "hPa"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "weather.barometric_pressure_convert",
"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
Zero and negative pressures are rejected as invalid_input because ambient barometric values are strictly positive physical quantities.
Input contract, response shape, and validation rules
On success the body echoes value and the normalised unit, then returns hpa, mb, inhg, and mmhg as rounded numbers, plus a short formula string documenting the fixed factors and a human-readable message that concatenates all four readings. Example: value 1013.25 with unit hPa returns matching hPa and mb of 1013.25, inHg near 29.921, and mmHg near 760. Keep requests small, pin the rounded fields in tests, and you get reproducible barometric unit tables for METAR notes, classroom worksheets, and edge workers without a full meteorological library. POST a JSON body with two required fields: value, a finite positive number for the pressure magnitude, and unit, a string naming the input scale. Accepted unit labels are hPa (with aliases such as hectopascal), mb (millibar, mbar), inHg (inches of mercury and common spacing variants), and mmHg (millimetres of mercury or torr). Field aliases such as amount, pressure, from, and from_unit are accepted so thin clients can reuse generic converter forms. Value may arrive as a JSON number or a numeric string; non-finite values, missing fields, empty strings, zero, and negative magnitudes fail with invalid_input and are not billed. Pair the response with your own charts if you need a multi-day pressure series; this endpoint converts a single snapshot only and does not fetch live weather, station altitude corrections, or QNH reductions.
Where a barometric pressure converter earns its keep
Hobbyist weather stations and home automation bridges often expose sensors in mb while dashboards expect inHg or hPa; a tiny deterministic converter keeps those pipelines honest without calling an external weather API just to rescale a number.
Technical questions
What does the barometric pressure converter cost?
The browser tool is free. API requests use prepaid KIT balance at $0.002 per successful call; invalid input is not billed.