Beaufort scale converter
Force 5, a fresh breeze, is 18.168656007245 knots. Convert wind between the Beaufort scale and knots, mph, m/s, km/h or ft/s in either direction, with the nearest force and all six units shown at once for sailing logs and weather briefings. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Value
- 5
- Source unit: beaufort
- beaufort
- Target unit: beaufort
- kn
- Result
- 18.1686560072 kn
- Converted
- 18.1686560072
- Value ms
- 9.3467641459
- Beaufort
- 5
A Beaufort scale converter turns a wind force number into knots, miles per hour, metres per second and related speed units—or the reverse—without memorizing marine tables or spreadsheet formulas. Enter a non-negative value plus a source unit and a target unit among Beaufort, knots, mph, m/s, km/h and ft/s; the tool returns the converted magnitude, the SI intermediate in metres per second, a multi-unit snapshot, the nearest integer force with its English description, and step-by-step substitution lines you can paste into a log or report. Sailors reading force reports, coastal weather briefings, outdoor event planners, and students converting homework values all need that same deterministic path.
What the Beaufort scale is and how conversion works
The Beaufort wind force scale ranks observed wind effects from calm through hurricane force using a number that mariners, meteorologists, and coastal operators still quote alongside instrumented speeds. This capability bridges that number and linear wind-speed units with a single deterministic model. For the force-to-speed direction it applies the widely cited World Meteorological Organization empirical relation: wind speed in metres per second equals zero point eight three six times the Beaufort number raised to the three-halves power.
The inverse raises the ratio of metres per second over zero point eight three six to the two-thirds power, giving a continuous Beaufort value you can round to the nearest integer for the classic force label.
Linear units among knots, miles per hour, metres per second, kilometres per hour, and feet per second convert through SI metres per second with exact international factors: the nautical mile of one thousand eight hundred fifty-two metres per hour for knots, the statute mile of one thousand six hundred nine point three four four metres per hour for mph, one thousand metres over three thousand six hundred seconds for km/h, and the international foot of zero point three zero four eight metres for feet per second.
Input Beaufort values must stay on the extended range zero through seventeen; negative magnitudes are rejected because force and wind speed here are non-negative quantities.
Practical tips, limits, and when to use this landing
Prefer sending bare numbers for value when you control the client; string numbers are accepted only when they match a strict finite numeric pattern without unit suffixes or thousand separators. Round-trip checks are straightforward: convert Beaufort five to knots and knots back to Beaufort and confirm you recover the original force within the published twelve-decimal rounding of the continuous path.
When teaching marine weather, pair classic examples such as force five (fresh breeze) to about eighteen knots under the WMO formula, twenty knots back to roughly five point three Beaufort, and ten metres per second to about twenty-two point four miles per hour with an implied force near five. Stay inside the absolute range so intermediate metres-per-second values cannot overflow, and keep Beaufort inputs at or below seventeen.
This landing targets people searching for a Beaufort scale converter, Beaufort to knots, wind force to mph, or Beaufort number to metres per second online; it is not a generic multi-quantity unit converter, not a weather forecast model, and not a gust-factor or local station correction tool.
What you can do with it
Marine logs and coastal briefings
Crews convert force numbers from forecasts into knots or m/s for instrument cross-checks, training simulators, and mixed-unit operational briefings.
Outdoor event and safety thresholds
Planners map anemometer mph or km/h readings to Beaufort labels so non-technical staff share a common wind-force language for hold or cancel decisions.
FAQ
Is Beaufort 13–17 allowed?
Yes for input force on the extended scale (maximum 17). Classical force names 0–12 are returned for rounded labels; 13–17 use extended hurricane-force wording.
Is the Beaufort scale converter free?
The browser tool is free and runs locally.
How many knots is Beaufort force 5?
About 18.168656007245 knots, a fresh breeze. The same result also appears as 9.346764145949 m/s, 20.908115931346 mph and 33.648350925417 km/h, so you can copy whichever unit your log or forecast uses.
What formula links the Beaufort number and wind speed?
The widely cited World Meteorological Organization relation: speed in m/s equals 0.836 times the force raised to the power 3/2. Going back, the force is the speed divided by 0.836, raised to the power 2/3.
What Beaufort force is 20 knots?
Roughly 5.3 on the continuous scale. The converter also rounds that to the nearest whole force, 5, and shows its classic description, fresh breeze, so you get both the precise value and the familiar label.
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/beaufort-wind \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"value":5,"from":"beaufort","to":"kn"}'const res = await fetch("https://api.kit.forhosting.com/conv/beaufort-wind", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"value": 5,
"from": "beaufort",
"to": "kn"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/conv/beaufort-wind",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"value": 5,
"from": "beaufort",
"to": "kn"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/conv/beaufort-wind", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"value":5,"from":"beaufort","to":"kn"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"value":5,"from":"beaufort","to":"kn"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/conv/beaufort-wind", 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": 5,
"from": "beaufort",
"to": "kn"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "conv.beaufort_wind",
"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.
Limits
max_abs | 1000000000000 |
beaufort_max | 17 |
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
Unknown unit names fail with a clear invalid_input error instead of silent wrong factors.
What the Beaufort scale is and how conversion works
Common aliases are accepted case-insensitively—bf, bft, and beaufort number for force; kn, kt, kts, and knots for kn; mi/h and miles per hour for mph; mps and metres per second for m/s; kmh and kph for km/h; fps and feet per second for ft/s. If the name is not on that list the solver rejects the request with invalid_input naming the bad field and listing supported units, so clients never guess whether a typo produced a wrong number.
How to call the API and read the response
Value must be a finite non-negative number or a strict numeric string within the published absolute limit of one trillion. Wire this into marine dashboards, weather widgets, mobile clients, or batch jobs that already hold a force or anemometer reading and only need a second representation for display, training, or regulatory comparison without shipping conversion tables in every app binary. Send a JSON body with three required fields: value (aliases amount, speed, force, v, and b), from (aliases from_unit, unit_from, and source), and to (aliases to_unit, unit_to, and target). From and to must resolve to supported unit names after alias normalization. On success the response echoes the rounded input value, canonical from and to labels, result and converted set to the same rounded target magnitude, value_ms as the SI intermediate, unit as the target label, beaufort as the continuous force implied by the intermediate speed, beaufort_rounded as the nearest integer force on the extended scale, description as the English force name, formula as a short equation string, message as an English summary, as as a full multi-unit snapshot of beaufort, kn, mph, m/s, km/h and ft/s, steps as ordered substitution lines, and supported_units as the six canonical identifiers. Failed validation—missing fields, non-finite or negative numbers, Beaufort above seventeen, values outside absolute limits, or an unknown unit name—returns invalid_input and is never charged. Pricing is a flat $0.002 per successful request with unit item and zero marginal unit price.
Practical tips, limits, and when to use this landing
Normalize display labels on your side if you need locale-specific spellings—this API always returns the short canonical tokens beaufort, kn, mph, m/s, km/h, and ft/s so automated tests stay stable. Prefer this capability when at least one endpoint is the Beaufort force or when you need force labels beside linear speeds; if you only need pure speed-to-speed conversion without Beaufort semantics, a dedicated speed converter may be enough. Failed tasks that return invalid_input do not consume prepaid balance, which keeps exploratory scripts cheap when clients deliberately probe unknown unit names.
Integration use cases
Homework and coding kata expected values
Students and developers generate deterministic Beaufort↔speed cases plus deliberate unknown-unit rejections for worksheets and unit tests.
Technical questions
What formula converts Beaufort number to wind speed?
This tool uses the WMO empirical relation v (m/s) = 0.836 × B^(3/2), and the inverse B = (v_ms / 0.836)^(2/3) for continuous force.
Which units are supported?
Beaufort (bf/bft), knots (kn), miles per hour (mph), metres per second (m/s), kilometres per hour (km/h), and feet per second (ft/s), with common aliases.
What happens if I send an unknown unit?
The API returns invalid_input naming the field and listing supported units. Failed tasks are not charged.