Units of Measurement

A comprehensive collection of units of measurement covering 121 physical quantities and 11 measurement systems. Available in both JSON and JSONL formats.

Files

The jsonl/ directory contains three JSONL files (one JSON object per line). The json/ directory contains the same datasets as JSON arrays.

`units_of_measurement.jsonl` (2,959 entries)

The comprehensive, merged dataset. This is the file most users will want. It combines the SI and UOM datasets below into a single superset with a unified schema covering all fields.

Fields:

Field	Type	Description
`unit`	string	Unit name (e.g., "kilometer", "pound")
`prefix`	string or null	SI prefix if applicable (e.g., "kilo", "milli")
`symbol`	string	Unit symbol (e.g., "km", "lb")
`plural`	string	Plural form (e.g., "kilometers", "pounds")
`property`	string	Physical quantity measured (e.g., "length", "mass")
`conversion_factor`	number	Multiplier to convert to the reference unit
`conversion_offset`	number	Additive offset for temperature conversions (present only for Celsius and Fahrenheit)
`reference_unit`	string	The SI coherent unit that `conversion_factor` is relative to
`alternate_unit`	array of strings	Alternate names for the unit (present only where applicable, e.g., "metre" for "meter")
`system`	string	Measurement system (see below)

`si_units.jsonl` (812 entries)

SI base units, SI derived units with special names, and non-SI units accepted for use with the SI (per the SI Brochure, 9th Edition). Each unit includes full SI prefix expansions (all 24 prefixes from quecto through quetta). Uses US English spellings ("meter", "liter").

Fields: unit, prefix, symbol, property, alternate_unit (optional), system

`uom.jsonl` (2,660 entries)

Units parsed from the Rust uom crate by Mike Boutin. Covers 117 physical quantities across multiple measurement systems, with conversion factors relative to the SI coherent unit for each quantity.

Fields: unit, symbol, plural, property, conversion_factor, conversion_offset (optional), reference_unit, system

Measurement Systems

System	Description
SI	International System of Units
Metric	Metric units not part of SI (e.g., bar, calorie, liter, tonne)
Imperial	British Imperial units (e.g., foot, pound, gallon)
CGS	Centimetre-Gram-Second system (e.g., dyne, erg)
Nautical	Nautical units (nautical mile, knot)
Astronomical	Astronomical units (astronomical unit, light year, parsec)
Atomic/Natural	Atomic and natural units (Bohr radius, hartree)
IEC	IEC binary prefixes for information (kibibyte, mebibyte, etc.)
Information	Information units (bit, byte, shannon, nat)
Ancient Roman	Historical Roman units of length, mass, area, and volume
other	Units not clearly belonging to a single system

Conversion Factors

Each entry's conversion_factor is the multiplier to convert one unit to the reference_unit for that property. For example:

kilometer: conversion_factor: 1000.0, reference_unit: "meter" -- 1 km = 1000 m
liter: conversion_factor: 0.001, reference_unit: "cubic meter" -- 1 L = 0.001 m^3
pound: conversion_factor: 0.4535924, reference_unit: "kilogram" -- 1 lb = 0.4536 kg

For temperature units with a conversion_offset, the conversion to the reference unit (kelvin) is: value_in_kelvin = value * conversion_factor + conversion_offset.

Usage

Install

npm install units-of-measurement   # Node.js
pip install units-of-measurement   # Python

Python

from units_of_measurement import load

units = load()  # 2,959 entries from the merged dataset

# Find all length units
length_units = [u for u in units if u["property"] == "length"]

# Convert 5 miles to meters
mile = next(u for u in units if u["unit"] == "mile")
meters = 5 * mile["conversion_factor"]  # 8046.72

# List all measurement systems
systems = sorted(set(u["system"] for u in units))

# Load a specific dataset
si = load("si_units")   # 812 SI entries
uom = load("uom")       # 2,660 uom entries

JavaScript

const { load } = require('units-of-measurement');
// or: import { load } from 'units-of-measurement';

const units = load(); // 2,959 entries from the merged dataset

// Find all mass units
const massUnits = units.filter(u => u.property === 'mass');

// Convert 10 pounds to kilograms
const pound = units.find(u => u.unit === 'pound' && u.property === 'mass');
const kg = 10 * pound.conversion_factor; // 4.535924

// Load a specific dataset
const si = load('si_units');
const uom = load('uom');

Raw Data (no package needed)

# Download as JSON array
curl -LO https://raw.githubusercontent.com/duncanscott/units-of-measurement/main/json/units_of_measurement.json

# Download as JSONL
curl -LO https://raw.githubusercontent.com/duncanscott/units-of-measurement/main/jsonl/units_of_measurement.jsonl

# Query JSON with jq — all Imperial length units
jq -c '.[] | select(.property == "length" and .system == "Imperial")' json/units_of_measurement.json

# Query JSONL with jq
jq -c 'select(.property == "length" and .system == "Imperial")' jsonl/units_of_measurement.jsonl

Data Sources

SI Brochure (9th Edition, 2019) -- Bureau International des Poids et Mesures (BIPM). Source for SI base units, derived units, and non-SI units accepted for use with the SI.
uom -- Units of Measurement Rust crate by Mike Boutin, licensed under MIT / Apache-2.0. Source for conversion factors, plurals, and extended unit coverage across multiple measurement systems. See THIRD-PARTY-LICENSES for the full license text.

License

This project is licensed under the MIT License.