Convert between measurement units
Length, mass, volume, area, speed, time, pressure, energy and temperature. SI and US customary units, with exact conversion factors.
How conversion works
Each unit is stored relative to the SI base for its category. We multiply by the source factor and divide by the destination factor. Temperatures route via Kelvin.
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Pick category
Length, mass, volume, area, speed, time, pressure, energy or temperature.
Parsing is strict-but-tolerant — comments and trailing commas are accepted on input where the source format historically permits them; output stays canonical.
catstricttolerantliveparsecat · sourcepick · liveLength
loaded · parsedtarget · ready - 02
Choose units
From and To dropdowns filter by category.
Conversion preserves type information where the target supports it (numbers stay numeric, booleans stay boolean) so the destination parser never has to re-coerce.
unitstype-preservinglosslesslivememoisedu · optionsu' · livemeter → foot
options applied · liveround-trip - 03
Type value
Decimals OK. Scientific notation OK.
Re-encoding is idempotent: running output back through the same converter produces the same bytes, which keeps round-trips git-friendly.
valueidempotentround-tripdiff-cleandeterministicv · convertedinput · ready100
converted · livediff-clean - 04
Read result
v · factor[from] / factor[to].
Copy writes via
navigator.clipboard.writeText; downloads use the target’s native MIME so editors apply the right syntax highlighting on open.calcclipboardtarget MIMEblobclient-side✓ · copiedready · done328.084 ft
shipped · ready to shipsuccess
Converting between formats, safely
Pick the strictest source format
Lossy formats hide bugs. Choose JSON or YAML as your source-of-truth, convert downstream as needed.
Round-trip in CI
If your converter is idempotent, your CI can verify A → B → A equals the original. Catches subtle data loss.
Numbers vs strings differ
YAML/TOML have a number type; CSV doesn’t. Quote IDs in CSV to keep leading-zero values intact.
Watch character encoding
Source format may be Latin-1 / Windows-1252; target should be UTF-8. Convert encoding before structure.
Preserve comments where you can
YAML and TOML support comments. Don’t silently drop them — they often encode intent.
Schema-aware beats blind
Use a schema to guide conversion. Field types, required-ness, and defaults survive better with structure.
When to convert units
Engineering, travel, recipes.
Engineering
Switch between SI and imperial on the fly. Type information survives: numbers stay numeric, booleans stay boolean, strings stay strings. The destination parser doesn't have to re-coerce, which avoids the "'true' becomes "true"" bug class.
round-trip safeTravel
Convert miles to km mid-trip. Run output back through the inverse converter to verify idempotent round-trips in CI. A → B → A should produce byte-identical input — if it doesn't, you've found data loss.
type-preservingRecipes
Convert cups to ml for international cooking. Comments and metadata survive where the target format supports them (YAML, TOML, HCL). The tool doesn't silently drop intent-encoded annotations, which keeps your config self-documenting.
schema-awareData tasks
Normalize incoming units before pipelines. Pair with a schema (JSON Schema, OpenAPI, Zod, Pydantic) to catch shape drift on either side. Catch breaking changes at conversion time rather than at runtime in production.
losslessLab work
Pressure psi ↔ kPa, energy J ↔ kcal. Output respects target-format conventions: quoting in CSV, indent in YAML, brackets in JSON. Existing parsers don't need patches, and the result drops into legacy pipelines unchanged.
diff-cleanGlobalisation
Localize a measurement for product copy. Encoding-aware: handles UTF-8 vs UTF-16 vs Latin-1 / Windows-1252 transparently. The character-set surprise that breaks "works on my machine" doesn't apply here.
i18nFrequently asked questions
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