Weight Converter API: The Complete Guide

Need to convert weight or mass units in your application? This guide covers everything you need to know about weight conversion via API, including metric and imperial units, conversion accuracy, and implementation examples in multiple languages.

Weight vs Mass

Technically, mass (measured in kilograms) and weight (measured in newtons) are different. However, in everyday usage and most applications, they're used interchangeably. The API handles common "weight" units that are technically measures of mass.

The metric system uses kilograms and grams, while the imperial system uses pounds and ounces. Converting between them is essential for international shipping, e-commerce, health apps, and cooking.

Supported Weight Units

Using the Weight Converter API

TinyFn provides a dedicated endpoint for weight conversions:

GET https://api.tinyfn.io/v1/convert/weight
Headers: X-API-Key: your-api-key

{
  "from_unit": "kg",
  "to_unit": "lb",
  "value": 75,
  "result": 165.347,
  "formula": "75 × 2.20462"
}

Parameters

Code Examples

JavaScript / Node.js

const response = await fetch(
  'https://api.tinyfn.io/v1/convert/weight?from=kg&to=lb&value=75',
  { headers: { 'X-API-Key': 'your-api-key' } }
);
const data = await response.json();
console.log(data.result); // 165.347

Python

import requests

response = requests.get(
    'https://api.tinyfn.io/v1/convert/weight',
    params={'from': 'kg', 'to': 'lb', 'value': 75},
    headers={'X-API-Key': 'your-api-key'}
)
data = response.json()
print(data['result'])  # 165.347

cURL

curl "https://api.tinyfn.io/v1/convert/weight?from=kg&to=lb&value=75" \
  -H "X-API-Key: your-api-key"

Common Use Cases

• E-commerce: Display product weights in local units
• Shipping: Calculate shipping costs based on weight
• Health Apps: Track weight in user-preferred units
• Recipe Apps: Convert ingredient weights
• Fitness: Track lifting weights and body weight

Best Practices

1. Know your audience: US users expect pounds, most others expect kg
2. Handle precision: Use appropriate decimal places
3. Store in metric: Store weights in kg internally, convert for display
4. Validate ranges: Check for reasonable weight values