Developer API

Free Unit Conversion API

Convert between 125+ units with a simple REST API. No authentication required. No signup needed.

Fast & Free

100 requests per day, no API key required

Simple REST API

GET request, JSON response, CORS enabled

No Auth Required

Start converting immediately, zero setup

Base URL

https://nextool.dev/api/v1

Convert Units

GET/api/v1/convert

Parameters

Parameter	Type	Required	Description
`from`	string	Yes	Source unit code (e.g., kg, lbs, mi, km, celsius)
`to`	string	Yes	Target unit code (e.g., lbs, kg, km, mi, fahrenheit)
`value`	number	No	Value to convert (default: 1)

Examples

Basic Conversion

Request

GET https://nextool.dev/api/v1/convert?from=kg&to=lbs&value=100

Response (200 OK)

{
  "from": {
    "unit": "kg",
    "label": "Kilograms",
    "value": 100
  },
  "to": {
    "unit": "lbs",
    "label": "Pounds",
    "value": 220.462
  },
  "formula": "1 kg = 2.20462 lbs",
  "toolUrl": "https://nextool.dev/convert/kg-to-lbs"
}

JavaScript / Fetch

JavaScript

const response = await fetch(
  "https://nextool.dev/api/v1/convert?from=mi&to=km&value=26.2"
);
const data = await response.json();
console.log(data.to.value); // 42.164808

Python / requests

Python

import requests

r = requests.get("https://nextool.dev/api/v1/convert", params={
    "from": "celsius",
    "to": "fahrenheit",
    "value": 37
})
data = r.json()
print(data["to"]["value"])  # 98.6

cURL

Terminal

curl "https://nextool.dev/api/v1/convert?from=gallons&to=liters&value=5"

List Available Conversions

Call the endpoint without parameters to get a list of all supported conversions:

Request

GET https://nextool.dev/api/v1/convert

Rate Limits

Plan	Limit	Price
Free	100 requests / 24 hours	$0
Pro	10,000 requests / 24 hours	$9/mo
Business	Unlimited	$29/mo

Error Codes

Code	Description
`400`	Missing or invalid parameters
`404`	Conversion not found
`429`	Rate limit exceeded (100/day on free tier)

Supported Categories

Weight

Length

Temperature

Volume

Area

Speed

Data

Time

Energy

Pressure

For the full interactive experience with charts and conversion tables, visit our conversion tools.

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