units-of-measurement 1.2.1

Comprehensive units of measurement dataset — 121 physical quantities, conversion factors, 11 measurement systems

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

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")
canonical_unit	string	Canonical name using · and / delimiters (e.g., watt/meter²·kelvin)
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")
quantity	string	Canonicalized physical quantity label (mirrors property)
dimension	object	SI base-exponent map (e.g., {"L": 1, "T": -1} for velocity); {} for dimensionless quantities
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)

The combination of unit and property is unique across all entries.

si_units.jsonl

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

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.

Dimension

The dimension field encodes each unit's SI base-quantity exponents as an object. The keys correspond to the seven SI base quantities:

Key	Base Quantity
L	length
M	mass
T	time
I	electric current
Θ	thermodynamic temperature
N	amount of substance
J	luminous intensity

Only non-zero exponents are included. For example, velocity (m/s) is {"L": 1, "T": -1} and power (W = kg·m²/s³) is {"M": 1, "L": 2, "T": -3}.

Dimensionless quantities — angle, solid angle, ratio, logarithmic ratio, and information — have an empty object {}. This follows SI convention: the radian and steradian are dimensionless derived units (dimension 1), and information units (bit, byte) fall outside the SI dimensional framework.

Usage

Install

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

Python

from units_of_measurement import load

units = load()  # all 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

# Canonical name & dimension vector for an acceleration unit
accel = next(u for u in units if u["unit"] == "meter per second squared")
accel["canonical_unit"]  # 'meter/second²'
accel["dimension"]       # {'L': 1, 'T': -2}
accel["quantity"] == accel["property"]  # True

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

# Load a specific dataset
si = load("si_units")   # SI entries
uom = load("uom")       # uom entries

JavaScript

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

const units = load(); // all 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

// Canonical representation + dimension vector
const accel = units.find(u => u.unit === 'meter per second squared');
console.log(accel.canonical_unit); // 'meter/second²'
console.log(accel.dimension);      // { L: 1, T: -2 }
console.log(accel.quantity === accel.property); // true

// 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.

Acknowledgments

This project was built with assistance from Claude (Anthropic) and Codex (OpenAI).

License

This project is licensed under the MIT License.