Convert physical and digital measurements across 80+ units
Convert physical and digital measurements across 80+ units with automatic category detection and full matrix breakdown
Request
- x-api-key: <your-api-key>
- Content-Type: application/json
Response
{
"category": "general",
"conversionMatrix": [
{
"formatted": "PL61 1090 1014 0000 0712 1981 2874",
"symbol": "€",
"unitKey": "example",
"unitName": "Ada Lovelace",
"value": 9.5
}
],
"input": {
"symbol": "€",
"unit": "EUR",
"unitName": "Ada Lovelace",
"value": 9.5
},
"result": {
"formatted": "PL61 1090 1014 0000 0712 1981 2874",
"symbol": "€",
"unit": "EUR",
"unitName": "Ada Lovelace",
"value": 9.5
},
"status": "success",
"tokensDeducted": 1
}What it does
Convert physical and digital measurements across 80+ units with automatic category detection and full matrix breakdown
Request
Body
| Field | Type | Required | Description |
|---|---|---|---|
category | enum | no | Optional physical dimension category. If omitted, will be auto-detected. One of: length, mass, temperature, volume, area, speed, pressure, energy…. |
fromUnit | string | yes | Source unit symbol or name (e.g. "km", "miles", "celsius", "fahrenheit", "lbs", "GiB", "psi", "kW") |
precision | integer | no | Number of significant digits for output formatting. |
toUnit | string | yes | Target unit symbol or name (e.g. "m", "feet", "kelvin", "kg", "MiB", "bar", "hp") |
value | number | yes | Numerical value to convert. |
Example request
{
"category": "length",
"fromUnit": "EUR",
"precision": 10,
"toUnit": "EUR",
"value": 9.5
}Response
| Field | Type | Description |
|---|---|---|
category | string | |
conversionMatrix | array<object> | Complete breakdown of this value converted across all supported units in this category |
↳ formatted | string | |
↳ symbol | string | |
↳ unitKey | string | |
↳ unitName | string | |
↳ value | number | |
input | object | |
↳ symbol | string | |
↳ unit | string | |
↳ unitName | string | |
↳ value | number | |
result | object | |
↳ formatted | string | |
↳ symbol | string | |
↳ unit | string | |
↳ unitName | string | |
↳ value | number | |
status | string | |
tokensDeducted | integer |
Example response
{
"category": "general",
"conversionMatrix": [
{
"formatted": "PL61 1090 1014 0000 0712 1981 2874",
"symbol": "€",
"unitKey": "example",
"unitName": "Ada Lovelace",
"value": 9.5
}
],
"input": {
"symbol": "€",
"unit": "EUR",
"unitName": "Ada Lovelace",
"value": 9.5
},
"result": {
"formatted": "PL61 1090 1014 0000 0712 1981 2874",
"symbol": "€",
"unit": "EUR",
"unitName": "Ada Lovelace",
"value": 9.5
},
"status": "success",
"tokensDeducted": 1
}Errors
Every error answers with the same envelope: an HTTP status, a machine code and a sentence.
400 | The body or a parameter failed validation. The details array names the field. |
401 | No key, a revoked key or a wrong header. Send x-api-key. |
402 | The wallet cannot cover this call. Top up or wait for the monthly grant. |
404 | The resource does not exist, or it is not yours. Both answer identically and cost nothing. |
429 | Over the per-minute quota of your tier. Back off and retry. |
5xx | Upstream refused or timed out. The call is not billed. |
Code
curl -X POST 'https://app.castomapi.com/v1/convert/units' \
-H 'x-api-key: <your-api-key>' \
-H 'Content-Type: application/json' \
-d '{"category": "length", "fromUnit": "EUR", "precision": 10, "toUnit": "EUR", "value": 9.5}'const res = await fetch('https://app.castomapi.com/v1/convert/units', {
method: 'POST',
headers: { 'x-api-key': '<your-api-key>', 'Content-Type': 'application/json' },
body: JSON.stringify({"category": "length", "fromUnit": "EUR", "precision": 10, "toUnit": "EUR", "value": 9.5})
});
const data = await res.json();
console.log(data);import { request } from 'node:https';
// Node 18+ has fetch built in
const res = await fetch('https://app.castomapi.com/v1/convert/units', {
method: 'POST',
headers: { 'x-api-key': '<your-api-key>', 'Content-Type': 'application/json' },
body: JSON.stringify({"category": "length", "fromUnit": "EUR", "precision": 10, "toUnit": "EUR", "value": 9.5})
});
const data = await res.json();
console.log(data);import requests
res = requests.post(
'https://app.castomapi.com/v1/convert/units',
headers={'x-api-key': '<your-api-key>'},
json={"category": "length", "fromUnit": "EUR", "precision": 10, "toUnit": "EUR", "value": 9.5},
timeout=30,
)
print(res.json())<?php
$ch = curl_init('https://app.castomapi.com/v1/convert/units');
curl_setopt_array($ch, [
CURLOPT_CUSTOMREQUEST => 'POST',
CURLOPT_RETURNTRANSFER => true,
CURLOPT_HTTPHEADER => ['x-api-key: <your-api-key>', 'Content-Type: application/json'],
CURLOPT_POSTFIELDS => json_encode(['category' => 'length', 'fromUnit' => 'EUR', 'precision' => 10, 'toUnit' => 'EUR', 'value' => 9.5]),
]);
$data = json_decode(curl_exec($ch), true);
print_r($data);Cost and limits
This operation needs no API key and costs nothing: called without a key it answers 200 and deducts zero tokens, up to 10 requests a minute per IP address.
Rate limits per minute
| No key | 10 |
| Free | 60 |
| Pro | 300 |
| Enterprise | 1200 |
Questions
What does Convert physical and digital measurements across 80+ units cost?
This operation needs no API key and costs nothing: called without a key it answers 200 and deducts zero tokens, up to 10 requests a minute per IP address.
How do I authenticate?
Send your key in the x-api-key header. One key covers every metered endpoint; there is nothing to enable per endpoint.
Can I send an Authorization: Bearer token instead?
Not for a metered endpoint — those take the x-api-key header and nothing else. Bearer tokens belong to the account side: the dashboard and account APIs accept a JWT session, and castomapi-auth issues those through a standard OAuth2 handshake, with authorization code, client credentials and refresh grants. The auth service page covers it.
What are the limits?
10 requests a minute per IP with no key at all, 60 a minute on the free tier, 300 on Pro, 1200 on Enterprise. Above the no-key tier the quota is per account, across every endpoint.
OpenAPI: https://app.castomapi.com/docs/json