About UnitConverter
A free, precision unit conversion tool
What We Do
UnitConverter is a free online tool that lets you convert between units of measurement across more than 80 categories. From everyday conversions like kilometres to miles and Celsius to Fahrenheit, to specialist engineering units like dynamic viscosity, surface tension, and magnetic flux density — everything is available in one place with no account required.
All calculations are performed instantly in your browser using precise mathematical constants validated against international standards including the International System of Units (SI), NIST reference data, and ISO 80000 series.
Our Features
- Live Currency Rates — 38 currencies updated via a multi-source API chain with automatic offline fallback, so conversions always work.
- 80+ Converter Categories — common units, engineering, fluids, heat, light, electricity, magnetism, radiology, and more.
- Bidirectional Input — type in either the "From" or "To" field and both update instantly.
- Quick Conversions — one-tap shortcuts for the most common unit pairs in each category.
- No Registration Required — completely free, no account, no subscription.
- Privacy First — no conversion data is ever transmitted to our servers.
Accuracy & Standards
Conversion factors are sourced from internationally recognised standards bodies including the Bureau International des Poids et Mesures (BIPM), the National Institute of Standards and Technology (NIST), and ISO. Where exact definitions exist (for example, 1 inch = exactly 0.0254 metres), we use those exact values. For derived units, we use the most precise published conversion factors available.
Currency conversions are inherently approximate due to continuously fluctuating market rates. Our currency data is sourced from financial data providers and is intended for informational and estimation purposes only, not for actual financial transactions.
Technology
UnitConverter is built with Next.js 14 and React 18. All unit conversion mathematics runs client-side in your browser — no data is sent to our servers during conversions. Currency rates are fetched through a server-side API proxy to keep API keys secure, and are cached to minimise unnecessary API calls.
How It's Funded
UnitConverter is completely free to use. The site is supported by advertising through Google AdSense. We have designed the site to show a minimal number of non-intrusive advertisements so they do not interfere with the conversion tool.
Contact & Feedback
We welcome reports of conversion errors, suggestions for new categories, and general feedback. Visit our Contact page to get in touch.