Temperature converter
One converter for the four temperature scales: 100 °C is 212 °F, and every result is checked against absolute zero so an impossible reading never reaches your report, recipe or lab notes. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Value
- 100
- From
- Celsius
- To
- Fahrenheit
- Result
- 212 °F
- Input
- 100
- Kelvin
- 373.15
Need a reliable temperature converter that understands all four common thermodynamic scales? Enter a number, choose the source scale and the target scale, and get an exact conversion between Celsius, Fahrenheit, Kelvin and Rankine. The calculator validates every reading against absolute zero so impossible temperatures never slip into a report, recipe, weather feed or lab notebook.
Which temperature scales you can convert
This temperature converter supports the four scales that appear most often in science, engineering and everyday life. Celsius is the SI-friendly everyday scale used by weather services outside the United States; zero marks the freezing point of water and one hundred marks boiling under standard conditions. Fahrenheit remains the civil scale in the US for weather, cooking and building controls, with water freezing at thirty-two and boiling at two hundred twelve.
Kelvin is the absolute thermodynamic scale required in physics and chemistry equations: zero Kelvin is absolute zero, the lowest temperature matter can reach. Rankine is the absolute scale built on Fahrenheit-sized degrees; it shows up in US aerospace and thermodynamic textbooks when engineers want absolute temperatures without switching to metric intervals. Convert freely among all four.
Identical-scale requests simply echo the value after the absolute-zero check, which is useful when you only need validation.
How conversion and absolute zero work
Every conversion routes through Kelvin as a thermodynamic hub, which avoids stacking formula errors when you jump from Fahrenheit to Rankine or Celsius to Kelvin. First the input is translated to Kelvin with the standard exact relations: Celsius plus two hundred seventy-three point one five, Fahrenheit plus four hundred fifty-nine point sixty-seven then multiplied by five ninths, Rankine multiplied by five ninths, and Kelvin left unchanged. The engine then checks that the Kelvin value is not negative.
Absolute zero is zero Kelvin, minus two hundred seventy-three point one five Celsius, minus four hundred fifty-nine point sixty-seven Fahrenheit, and zero Rankine.
What you can do with it
Lab and process control logs
Normalize sensor dumps that mix Celsius and Kelvin into a single scale before charting, alarming or long-term storage.
Weather and travel apps
Show local outdoor temperatures in the visitor’s preferred scale while keeping Kelvin available for scientific overlays.
Engineering homework and documentation
Convert between Fahrenheit and Rankine or Celsius and Kelvin when preparing thermodynamic tables, reports and graded exercises.
FAQ
Can I convert 100 °C to Fahrenheit?
Yes. Send value 100, from celsius and to fahrenheit; the result is 212 with unit °F and the equivalent Kelvin value included.
What is the formula from Celsius to Fahrenheit?
Multiply the Celsius value by 9/5 and add 32. That is why water freezes at 32 °F and boils at 212 °F, the same points as 0 °C and 100 °C.
How do I convert Celsius to Kelvin?
Add 273.15 to the Celsius value. Kelvin has the same step size as Celsius but starts at absolute zero, so it never goes below zero.
What is absolute zero on each scale?
It is 0 K, which equals -273.15 °C, -459.67 °F and 0 °R. The converter rejects any reading below that point, because no temperature can be colder.
What is the Rankine scale used for?
Rankine is an absolute scale with Fahrenheit-sized degrees. It appears in US engineering and thermodynamics books when absolute temperatures are needed without switching to metric.
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/conv/temperature \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"value":100,"from":"celsius","to":"fahrenheit"}'const res = await fetch("https://api.kit.forhosting.com/conv/temperature", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"value": 100,
"from": "celsius",
"to": "fahrenheit"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/conv/temperature",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"value": 100,
"from": "celsius",
"to": "fahrenheit"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/conv/temperature", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"value":100,"from":"celsius","to":"fahrenheit"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"value":100,"from":"celsius","to":"fahrenheit"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/conv/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
{
"value": 100,
"from": "celsius",
"to": "fahrenheit"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "conv.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
Run it free in the browser or call the same logic through the API at $0.002 per request with no subscription.
Which temperature scales you can convert
Short aliases such as C, F, K and R are accepted alongside the full names so scripts and forms stay concise.
How conversion and absolute zero work
Any reading below that floor returns an invalid_input error and is not charged, because the client supplied a physically impossible temperature rather than a service fault.
Using the API, pricing and delivery
Call the capability with three fields: value as a finite number, from as the source scale, and to as the target scale. The response includes the normalized input, the canonical from and to scale names, the converted result, a display unit such as degree C or K, and the intermediate Kelvin value so auditors can recompute the step by hand. Status is beta while the surface stabilizes, but the arithmetic itself follows the same fixed formulas used in textbooks and will not change under the same inputs. Pricing for the hosted API is a flat $0.002 per successful request; failed validation such as a missing field or a temperature below absolute zero does not consume balance. For pipelines, submit each conversion as an independent task and collect results through your usual webhook or signed link flow. Keep source and destination scales explicit in your integration rather than inferring them from symbols in free text: that contract keeps SDK types, OpenAPI schemas and form controls aligned, and it prevents silent misreads when a feed mixes metric and imperial symbols.
Technical questions
Which temperature scales are supported?
Celsius, Fahrenheit, Kelvin and Rankine. Full names and short aliases such as C, F, K and R are accepted and normalized in the response.
What happens if the value is below absolute zero?
The request fails with invalid_input explaining that the temperature is below absolute zero. Invalid client input is not charged.
How much does the temperature converter API cost?
Each successful API call costs $0.002. The same converter runs free in your browser with no account required.
Is the conversion deterministic?
Yes. The math uses fixed formulas through Kelvin and six-decimal rounding, so the same input always yields the same JSON result.