Thermal resistance converter
1 K/W is 0.52752792631 °F·h/BTU, and 1 °C/W is exactly 1 K/W. Convert a thermal resistance between heatsink datasheets, SI models and imperial insulation tables, and see the same value in all three units at once. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Amount
- 1
- Input unit
- k_w
- Output unit
- f_h_btu
- Result
- 0.5275279263
- K per w
- 1
- C per w
- 1
- F h per btu
- 0.5275279263
Thermal resistance conversion between SI kelvin per watt, the everyday Celsius per watt used on heatsink and semiconductor datasheets, and the imperial Fahrenheit-hour per BTU still printed on HVAC and building-insulation tables is a daily chore in electronics cooling homework, thermal interface material comparisons, enclosure design, and lab reports. People search for a thermal resistance converter when they need K/W next to °C/W, or °C/W next to °F·h/BTU, not a general multi-unit toolbox that also handles length and temperature. This capability accepts one finite amount plus from and to unit labels among those three families, bridges every conversion through kelvin per watt so results stay consistent, and returns the target value together with the same thermal resistance expressed in all three units. Unrecognized unit names are rejected with a clear validation error instead of silently guessing a nearby symbol.
How the thermal resistance converter maps SI and imperial units through K/W
Start from the kelvin per watt as the SI coherent unit of thermal resistance R_th equals temperature rise over heat flow and express every other unit as a fixed factor into K/W. One degree Celsius per watt equals exactly one kelvin per watt because a temperature difference of one degree Celsius is identical to a difference of one kelvin; no absolute-zero offset enters the algebra.
One international-table British thermal unit path gives Fahrenheit-hour per BTU equal to about 1.89563424063 kelvin per watt after dividing five-ninths kelvin per Fahrenheit degree by the watt equivalent of one IT BTU per hour. This calculator never mixes those paths ad hoc. It multiplies the input amount by the factor of the source unit to reach K/W, then divides by the factor of the target unit to produce the result.
Because every path shares the same intermediate, converting one K/W into °F·h/BTU and back, or comparing a heatsink °C/W rating to an imperial insulation table, stays numerically consistent within ordinary floating-point precision. The tool does not convert thermal conductivity in watts per meter-kelvin, does not compute U-values or areal R-values of walls, does not solve junction-to-ambient networks with multiple nodes, and does not fetch weather or material databases.
It answers only the algebraic thermal resistance unit conversion people mean when they type thermal resistance converter into a search bar and expect K/W, °C/W, and °F·h/BTU.
Where dedicated thermal resistance conversion shows up in real work
Secondary-school and college heat-transfer courses constantly assign problems that give a component thermal resistance on one scale and ask for another, often mixing SI K/W with imperial °F·h/BTU on the same worksheet. Electronics and power-module teams quote heatsinks, TIM pads, and package junction-to-case ratings in °C/W while SI-native models and academic papers expect K/W, so a single conversion pass keeps spreadsheets, SPICE macros, and sensors aligned.
HVAC and building-energy groups still see Fahrenheit-hour per BTU on older equipment tables; procurement and test scripts normalize those figures into K/W before comparing parts. If you later need thermal conductivity, heat-transfer coefficient, areal building R-value, or a general multi-category unit toolbox, treat those as separate search intents and landings rather than overloading this thermal resistance converter page.
What you can do with it
Heatsink and semiconductor datasheets
Normalize junction-to-ambient and heatsink ratings between °C/W and K/W so SI models and vendor tables stay consistent.
HVAC and insulation tables
Convert imperial °F·h/BTU thermal resistance figures into K/W for design tools, compliance checks, and mixed-unit reports.
FAQ
What happens if I send an unrecognized unit?
The error message includes Unrecognized unit and lists the supported families so you can correct the label.
Is °C/W the same as K/W?
Yes for temperature differences. One degree Celsius of rise equals one kelvin of rise, so 1 °C/W equals 1 K/W exactly. Absolute temperature offsets are not applied.
Which BTU definition does it use?
The international-table BTU (1055.05585262 J). Combined with five-ninths kelvin per Fahrenheit degree, 1 °F·h/BTU ≈ 1.89563424063 K/W.
What does it cost?
The browser tool is free and runs locally.
Does it add up the resistances of a heatsink, a pad and a package?
No. It converts one thermal resistance value from one unit to another. Junction-to-ambient networks with several layers, wall U-values and areal R-values are outside this converter.
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/thermal-resistance \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"amount":1,"from":"k_w","to":"f_h_btu"}'const res = await fetch("https://api.kit.forhosting.com/conv/thermal-resistance", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"amount": 1,
"from": "k_w",
"to": "f_h_btu"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/conv/thermal-resistance",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"amount": 1,
"from": "k_w",
"to": "f_h_btu"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/conv/thermal-resistance", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"amount":1,"from":"k_w","to":"f_h_btu"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"amount":1,"from":"k_w","to":"f_h_btu"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/conv/thermal-resistance", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"amount": 1,
"from": "k_w",
"to": "f_h_btu"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "conv.thermal_resistance",
"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
What you send and what you get back from the API and browser form
Send three fields: amount, a finite number for the thermal resistance magnitude; from, a string naming the input unit; and to, a string naming the output unit. When a unit string is unknown the error message includes Unrecognized unit and lists the three supported families so clients can fix the label rather than guessing. Classic checks include one °C/W becoming exactly one K/W, one K/W becoming roughly 0.5275 °F·h/BTU, and one °F·h/BTU matching about 1.8956 K/W. Both unit fields accept short keys and everyday words in any common casing, including k_w or K/W or kelvin per watt, c_w or C/W or celsius per watt, and f_h_btu or F h/BTU or fahrenheit hour per BTU. Missing fields, non-numeric amount strings, NaN, Infinity, and unrecognized unit labels fail with invalid_input and are not charged. On success the response echoes the cleaned amount, normalized from and to keys, the primary result in the target unit, the same resistance as k_per_w, c_per_w, and f_h_per_btu with twelve significant digits of stable precision, the SI factors used, the formula string, and method kw_bridge. Pricing for successful API calls is the published base of $0.002 per item; validation failures do not consume prepaid balance.
Where dedicated thermal resistance conversion shows up in real work
Data pipelines that ingest mixed lab or IoT payloads with C/W and K/W tags can call this capability once per reading instead of reimplementing the factors in every service. Because this capability is a pure parse engine, API pricing is the published base of $0.002 per successful item and failed validation does not consume balance.
Integration use cases
Homework and curriculum tools
Map exam values between K/W, °C/W, and °F·h/BTU for answer keys, auto-graders, and interactive heat-transfer demos that share one JSON contract.
Technical questions
Which thermal resistance units does this converter support?
Kelvin per watt (K/W, k_w), Celsius per watt (°C/W, c_w), and Fahrenheit hour per BTU (°F·h/BTU, f_h_btu). Common aliases are accepted; the response normalizes to short keys.