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Old wind chill calculator

A 10 m/s wind on air at 10 °C gives a Siple–Passel cooling power of about seven hundred thirty-eight kilocalories per square metre per hour. It is the classic 1945 index, not a modern feels-like temperature. Free in your browser.

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Worked example

If you enter

Wind speed: 10
Temperature difference: 23

You get

Air temperature c: 10
Skin temperature c: 33
Cooling factor: 32.0727766017
Wind chill index: 737.6738618387

Before modern “feels-like” wind-chill temperatures, polar researchers Siple and Passel published a 1945 cooling-power formula that still appears in textbooks, climate history notes, and side-by-side comparisons with today’s National Weather Service charts. This old wind chill calculator accepts wind speed in metres per second and the skin-to-air temperature difference ΔT equals 33 minus air temperature in degrees Celsius, then evaluates the classic product of the Siple–Passel cooling factor and that temperature difference. The result is a wind chill index in kilocalories per square metre per hour—a cooling-power measure, not a pseudo-temperature.

What the 1945 Siple and Passel wind chill index measures

The Siple and Passel experiments measured how quickly heat left a water-filled plastic cylinder exposed to Antarctic wind, and fitted a simple algebraic model that became the standard wind chill index for decades.

In SI-friendly form the cooling power is written WCI equals open parenthesis 10.45 plus 10 times the square root of v minus v close parenthesis times open parenthesis 33 minus Ta close parenthesis, where v is wind speed in metres per second, Ta is air temperature in degrees Celsius, and 33 degrees Celsius is the assumed skin temperature.

The first parenthesis is a cooling factor that rises quickly as calm air becomes a light breeze, then rolls over at higher speeds; the second parenthesis is the driving temperature difference from warm skin to cold air. Multiplying them yields a positive cooling power in kilocalories per square metre per hour when air is colder than skin.

Modern operational products replaced this index with empirical “equivalent temperature” charts tuned to face heat loss and walking speeds, but the 1945 expression remains the reference many papers still quote when they say “old wind chill.” Use it when you need the historical cooling-power number itself, or when you must show students how an older index differs in shape and units from today’s feels-like temperature.

What you can do with it

Classroom comparison with modern wind chill

Compute the 1945 Siple–Passel cooling power next to a modern feels-like temperature so students see different units, shapes, and assumptions.

Historical station-log reanalysis

Batch re-evaluate archived wind and temperature pairs under the classic index for climate-history or polar field notebooks.

FAQ

What formula does this old wind chill calculator use?

The classic Siple and Passel (1945) cooling power: WCI = (10.45 + 10√v − v) × (33 − Ta), with v in m/s and temperatures in °C.

Is the result a feels-like temperature?

Modern NWS-style wind-chill temperatures use a different empirical model.

Why are negative wind speed or temperature difference rejected?

Negative wind speed is unphysical in this model.

How do I enter the temperature difference?

Subtract the air temperature in °C from 33, the classic skin temperature. Air at 10 °C gives a difference of 23, and air already at 33 °C gives zero.

How do I convert km/h or mph to metres per second?

Divide kilometres per hour by 3.6, or multiply miles per hour by 0.44704, before entering the wind speed. The 1945 formula works in metres per second.

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

POSThttps://api.kit.forhosting.com/earth/wind-chill-old

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/earth/wind-chill-old \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"wind_speed":10,"temperature_difference":23}'

const res = await fetch("https://api.kit.forhosting.com/earth/wind-chill-old", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "wind_speed": 10,
    "temperature_difference": 23
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/earth/wind-chill-old",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "wind_speed": 10,
    "temperature_difference": 23
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/earth/wind-chill-old", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"wind_speed":10,"temperature_difference":23}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"wind_speed":10,"temperature_difference":23}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/earth/wind-chill-old", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "wind_speed": 10,
  "temperature_difference": 23
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "earth.wind_chill_old",
  "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

Per request$0.002

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

Negative wind speed or a negative temperature difference is rejected with invalid_input so scripts never silently invent a heating rate.

Input contract, units, and error behaviour

Wind speed must be non-negative—negative speed has no physical meaning in this model and is rejected. Temperature difference must also be non-negative: a negative ΔT would mean air warmer than the classic skin temperature, which sits outside the original cooling-power framing and is rejected rather than returned as a signed “heating index.” Example: ten metres per second wind with ΔT of twenty-three degrees Celsius (air about ten degrees Celsius) yields a large positive cooling power you can plot against modern wind-chill temperature for the same conditions. POST a JSON object with two required finite numbers. wind_speed is the wind velocity v in metres per second; convert from kilometres per hour by dividing by 3.6, or from miles per hour by multiplying by 0.44704, before you call the endpoint. temperature_difference is ΔT equals 33 minus Ta in degrees Celsius: if air is minus ten degrees Celsius, send twenty-three; if air is already thirty-three degrees Celsius, send zero. Both fields may arrive as JSON numbers or numeric strings; missing, blank, or non-finite values fail with invalid_input naming the field. On success the body echoes the rounded inputs, reports implied air_temperature_c as thirty-three minus ΔT, exposes cooling_factor as 10.45 plus 10√v minus v, and returns wind_chill_index with unit kcal/(m2·h). formula and equation strings restate the Siple–Passel identity for display, and steps walks through substitution for teaching UIs. Failed validation is not billed; successful analytic calls use the published $0.002 base price with no model tokens and no outbound network.

Where a classic wind chill API earns its keep

Meteorology instructors need a deterministic oracle that reproduces the textbook 1945 index so lab write-ups can compare old cooling power with new feels-like charts without spreadsheet drift. Keep wind speed in m/s, keep ΔT non-negative, pin rounded outputs in tests, and you get reproducible historical wind-chill indices for courses, docs, and edge workers without standing up a full weather library of your own. Climate-history and polar-science notebooks often re-evaluate archived station logs that recorded wind and temperature under the Siple–Passel convention; calling a tiny parse API avoids re-implementing the square-root factor in every language. Emergency-management and outdoor-education materials sometimes show both indices side by side so readers understand why older guidance used different numbers; this endpoint supplies the legacy column only.

Integration use cases

SEO widget and API parity

Power an “old wind chill calculator” landing page whose free browser results match the prepaid API at $0.002 per successful call.

Technical questions

What units should I use for wind speed?

Metres per second (m/s). Convert km/h by dividing by 3.6, or mph by multiplying by about 0.44704, before calling the API.

What does the Siple–Passel wind chill calculator cost?

The browser tool is free. API requests use prepaid KIT balance at $0.002 per successful call; invalid input is not billed.

Read the full KIT documentation →

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