Radiant intensity converter
Switch power per solid angle between six units: 1 W/sr is 1000 mW/sr, and square-degree values use the exact solid-angle bridge, so laser datasheets, calibration sheets and instrument notes speak one unit. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Value
- 1
- From
- W sr
- To
- Mw sr
- Result
- 1,000
- From label
- watts per steradian
- To label
- milliwatts per steradian
- W sr
- 1
A radiant intensity converter turns a radiometric power-per-solid-angle quantity written in one unit into another without hunting tables or rewriting spreadsheet formulas.
Supported units and how the conversion is computed
Prefix factors are exact SI powers of ten: one milliwatt per steradian is one thousandth of a watt per steradian, one microwatt per steradian is one millionth, and one kilowatt per steradian is one thousand watts per steradian. Square-degree forms use the geometric solid-angle identity that one square degree equals (π/180)² steradians, so one watt per square degree equals (180/π)² watts per steradian—the same bridge used in solid-angle conversion.
Because the intermediate is always W/sr, converting A to B and B to A is consistent up to the published rounding of twelve decimal places, and there is no pairwise matrix that can drift out of sync. Luminous intensity in candela, radiance in W/(sr·m²), irradiance in W/m², and bare radiant flux in watts are intentionally out of scope so optical engineers, remote-sensing analysts, and physics students get predictable intensity-only results under one clear radiometric convention.
Where radiant intensity conversions come up
Use the free in-browser radiant intensity converter when you need a quick watts-per-steradian to milliwatts-per-steradian, milliwatts-per-steradian to watts-per-square-degree, or microwatts-per-steradian check while reading a laser datasheet, radiometer calibration sheet, remote-sensing product note, astronomy detector brief, lab procedure, or homework problem. Open the page, enter the number and units, and copy the result without installing a spreadsheet, a unit library, or a desktop calculator pack. Source inputs follow the same retention rules as other KIT parse items, and results are safe to cache because the algorithm is fully deterministic.
Authors shipping mobile apps or chatbots can map the result and formula fields directly into cards that show both the number and the conversion path students, technicians, and optical engineers expect on paper.
What you can do with it
Laser and LED radiometric datasheets
Convert milliwatts per steradian peak ratings to watts per steradian so emitters, collimators, and module specs share one SI intensity view without hand-written factors.
Remote sensing and astronomy instruments
Normalize W/sr and W/deg² figures in calibration tables, detector FOV notes, and product documentation when drawings mix SI steradian bases and square-degree beam solid angles.
FAQ
What happens if I send an unknown unit?
The message names the field and lists supported units. Validation failures are not charged.
Is the radiant intensity converter free?
The browser tool runs free on your device.
How many mW/sr are in 1 W/sr?
Exactly 1000. Milli means one thousandth, so one watt per steradian is a thousand milliwatts per steradian, and one microwatt per steradian is one millionth of a watt per steradian.
How are watts per square degree turned into watts per steradian?
One square degree is (π/180)² steradians, so one watt per square degree equals (180/π)² watts per steradian. The converter applies that geometric identity exactly instead of a rounded table value.
Can it convert candela, radiance or irradiance?
No. It handles radiant intensity only. Candela measures luminous intensity, radiance adds a per-area term and irradiance is power per area, so each one needs a different conversion.
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/radiant-intensity \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"value":1,"from":"w_sr","to":"mw_sr"}'const res = await fetch("https://api.kit.forhosting.com/conv/radiant-intensity", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"value": 1,
"from": "w_sr",
"to": "mw_sr"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/conv/radiant-intensity",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"value": 1,
"from": "w_sr",
"to": "mw_sr"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/conv/radiant-intensity", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"value":1,"from":"w_sr","to":"mw_sr"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"value":1,"from":"w_sr","to":"mw_sr"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/conv/radiant-intensity", 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": 1,
"from": "w_sr",
"to": "mw_sr"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "conv.radiant_intensity",
"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
The browser tool runs free on your device; the prepaid API charges $0.002 per successful item when pipelines need the same contract from servers and automation.
Supported units and how the conversion is computed
The converter accepts six radiant intensity families under stable canonical codes: w_sr for watts per steradian (the SI radiometric intensity unit), mw_sr for milliwatts per steradian, uw_sr for microwatts per steradian, kw_sr for kilowatts per steradian, w_deg2 for watts per square degree, and mw_deg2 for milliwatts per square degree. Friendly aliases such as W/sr, mW/sr, µW/sr, kW/sr, W/deg², W/deg^2, watts per steradian, milliwatts per square degree, and similar slash or full-name forms are normalized case-insensitively so forms and APIs can pass either short codes or written names. Every request multiplies the input value by the exact watts-per-steradian factor for the source, then divides by the watts-per-steradian factor for the target.
Request shape, response fields, and unknown-unit errors
The error message names the bad field and lists the supported set so clients can correct forms without guessing. Negative values are allowed when you need signed or relative intensity differences in analysis pipelines; zero converts cleanly to zero in every target unit. Send a JSON body with three required fields: value as a finite number, from as the source unit string, and to as the target unit string. Aliases amount and quantity are accepted for value; unit_from and source for from; unit_to and target for to. On success the response echoes the canonical from and to codes, human-readable from_label and to_label strings, the converted result, the intermediate w_sr quantity in watts per steradian, the dimensionless factor from source to target, a short formula line suitable for UI display, the method tag radiant_intensity_si, and the fixed list of units_supported. Missing value, non-finite numbers such as NaN or Infinity, missing unit fields, and any token that does not map to a supported unit fail with invalid_input and are not charged after the engine rejects the request. Identical inputs always yield identical JSON because the path is pure arithmetic with no randomness, no remote lookup, and no dependence on the wall clock, which makes the endpoint safe to pin in continuous-integration goldens and SDK contract tests. Microwatt-scale detector peaks and kilowatt-per-steradian laser figures share the same code path, so extreme magnitude pairs remain well-defined as long as IEEE double precision can represent the intermediate product.
Browser use, API pricing, and everyday workflows
Switch to the prepaid API when an optical design plugin, radiometric LIMS, satellite instrument pipeline, LED or laser product configurator, physics homework checker, or instrumentation tool must convert radiant intensity at scale under a stable KIT contract at $0.002 per successful item; validation failures that raise invalid_input do not consume balance after rejection. Pair this endpoint with solid-angle or luminous-intensity tools when a product pipeline needs several measure families, or call it alone when search traffic is specifically for radiant intensity conversion—W/sr, mW/sr, µW/sr, kW/sr, and per-square-degree forms—rather than a general unit switchboard.
Integration use cases
Lab homework and API automation
Convert microwatts per steradian and kilowatts per steradian for class problems and instrument pipelines with a prepaid, deterministic API and clear invalid_input on unknown units.
Technical questions
Which radiant intensity units does this converter support?
Watts per steradian (w_sr), milliwatts per steradian (mw_sr), microwatts per steradian (uw_sr), kilowatts per steradian (kw_sr), watts per square degree (w_deg2), and milliwatts per square degree (mw_deg2). Full names and common aliases are accepted; unknown units raise invalid_input.
How many milliwatts per steradian is one watt per steradian?
Exactly 1000 mW/sr. Send value: 1, from: "w_sr", to: "mw_sr" to see it in the result field.
How do I convert 1 W/sr to watts per square degree?
Send JSON with value: 1, from: "w_sr", to: "w_deg2". The response uses 1 deg² = (π/180)² sr, so result is (π/180)² W/deg², plus a w_sr intermediate and a readable formula.