Heat flux density converter
A heat flux of 1000 W/m² is about 317 BTU per hour per square foot, or 0.1 W/cm². Enter one value and see it in all four units at once, for building envelopes, heaters, solar simulators and lab reports. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Amount
- 1,000
- Input unit
- w_m2
- Output unit
- btu_h_ft2
- Result
- 316.998330628
- W per m2
- 1,000
- W per cm2
- 0.1
- Btu per h ft2
- 316.998330628
Heat flux density conversion between SI watts per square meter, the compact watts per square centimeter scale used on high-intensity heaters and solar simulators, the still-common imperial BTU per hour square foot used in building envelopes and HVAC ratings, and the calorie per second square centimeter scale found in older thermal-physics tables is a daily chore in heat-transfer homework, building-energy models, solar and laser process sheets, and lab reports. People search for a heat flux density converter when they need W/m² next to BTU/(h·ft²), or W/cm² next to cal/(s·cm²), 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 four families, bridges every conversion through watts per square meter so results stay consistent, and returns the target value together with the same heat flux density expressed in all four units. Unrecognized unit names are rejected with a clear validation error instead of silently guessing a nearby symbol.
How the heat flux density converter maps SI, imperial, and calorie units through W/m²
Start from the watt per square meter as the SI coherent unit of heat flux density q double prime and express every other unit as a fixed factor into W/m². One watt per square centimeter is exactly ten thousand watts per square meter because one square meter holds ten thousand square centimeters. One international-table British thermal unit per hour per square foot equals about 3.154590745 watts per square meter after dividing the IT watt equivalent of one BTU per hour by the square of the international foot.
One thermochemical calorie per second per square centimeter is exactly forty-one thousand eight hundred forty watts per square meter because one thermochemical calorie is 4.184 joules, so one calorie per second is 4.184 watts, and that power over one square centimeter scales by ten thousand into W/m². This calculator never mixes those paths ad hoc. It multiplies the input amount by the factor of the source unit to reach W/m², then divides by the factor of the target unit to produce the result.
Because every path shares the same intermediate, converting one thousand W/m² into BTU per hour square foot and back, or comparing W/cm² to cal/(s·cm²), stays numerically consistent within ordinary floating-point precision. The tool does not convert total heat power in bare watts without an area, does not compute U-values or thermal conductivity, does not integrate transient heat loads over time, and does not fetch weather or solar irradiance databases.
It answers only the algebraic heat flux density unit conversion people mean when they type heat flux density converter into a search bar and expect W/m², W/cm², BTU/(h·ft²), and cal/(s·cm²).
Where dedicated heat flux density conversion shows up in real work
Secondary-school and college heat-transfer courses constantly assign problems that give a surface heat flux on one scale and ask for another, often mixing SI W/m² with imperial BTU per hour square foot on the same worksheet. Building-energy and HVAC teams quote envelope heat gains and radiant panels in BTU/(h·ft²) while design tools and SI-native models expect W/m², so a single conversion pass keeps load calculations, code compliance tables, and sensors aligned.
Solar-process, laser, and high-intensity heater manufacturers publish flux maps in W/cm²; procurement and test scripts normalize those maps into W/m² before comparing parts or stacking with irradiance products. Older thermal-physics and calorimetry tables still list cal/(s·cm²), and modern lab notebooks need consistent SI export. If you later need total heat power without area, U-value conversion, thermal conductivity, or a general multi-category unit toolbox, treat those as separate search intents and landings rather than overloading this heat flux density converter page.
What you can do with it
HVAC and building envelope loads
Normalize radiant panels, solar gains, and envelope heat fluxes between W/m² and BTU/(h·ft²) so SI models and imperial code tables stay consistent.
Process heaters and solar simulators
Convert high-intensity flux maps between W/cm² and W/m² for datasheets, test scripts, and safety zone labels without hand-written factors.
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.
How many W/m² are in one W/cm²?
Exactly 10_000. One square meter holds ten thousand square centimeters, so the SI conversion is exact.
Which calorie and BTU definitions does it use?
Thermochemical calorie (4.184 J) for cal/(s·cm²), giving exactly 41_840 W/m², and the international-table BTU with the international foot for BTU/(h·ft²) ≈ 3.154590745 W/m².
What does it cost?
The browser tool is free and runs locally.
Can it convert total heat in watts or a U-value?
No. It converts heat flux density only, which is power per unit of area. Total power in bare watts, U-values, thermal conductivity and heat loads that change over time all need other tools.
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/heat-flux \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"amount":1000,"from":"w_m2","to":"btu_h_ft2"}'const res = await fetch("https://api.kit.forhosting.com/conv/heat-flux", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"amount": 1000,
"from": "w_m2",
"to": "btu_h_ft2"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/conv/heat-flux",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"amount": 1000,
"from": "w_m2",
"to": "btu_h_ft2"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/conv/heat-flux", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"amount":1000,"from":"w_m2","to":"btu_h_ft2"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"amount":1000,"from":"w_m2","to":"btu_h_ft2"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/conv/heat-flux", 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": 1000,
"from": "w_m2",
"to": "btu_h_ft2"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "conv.heat_flux",
"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 heat flux density 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 four supported families so clients can fix the label rather than guessing. Classic checks include one W/cm² becoming ten thousand W/m², one thousand W/m² becoming roughly three hundred seventeen BTU per hour square foot, and one cal per second square centimeter matching forty-one thousand eight hundred forty W/m² exactly. Both unit fields accept short keys and everyday words in any common casing, including w_m2 or W/m2 or watt per square meter, w_cm2 or W/cm2 or watt per square centimeter, btu_h_ft2 or BTU/h ft2 or btu per hour square foot, and cal_s_cm2 or cal/s cm2 or calorie per second square centimeter. 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 density as w_per_m2, w_per_cm2, btu_per_h_ft2, and cal_per_s_cm2 with twelve significant digits of stable precision, the SI factors used, the formula string, and method wm2_bridge. Pricing for successful API calls is the published base of $0.002 per item; validation failures do not consume prepaid balance.
Where dedicated heat flux density conversion shows up in real work
Data pipelines that ingest mixed IoT or lab payloads with W/m2, W/cm2, and BTU 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 W/m², W/cm², BTU/(h·ft²), and cal/(s·cm²) for answer keys, auto-graders, and interactive heat-transfer demos that share one JSON contract.
Technical questions
Which heat flux density units does this converter support?
Watts per square meter (W/m², w_m2), watts per square centimeter (W/cm², w_cm2), BTU per hour square foot (BTU/(h·ft²), btu_h_ft2), and calories per second square centimeter (cal/(s·cm²), cal_s_cm2). Common aliases are accepted; the response normalizes to short keys.