Unit Converter
Convert between units of length, weight, temperature, speed, and data.
About This Tool
Instantly convert between common units across five categories: length, weight, temperature, speed, and data storage. Simply select a category, choose your source and target units, and see the result update in real time as you type. Conversions use standard conversion factors with full floating-point precision, making this tool suitable for engineering, cooking, science, and everyday tasks. Works entirely offline once loaded, with no server calls or sign-up required.
What you provide
Category, source unit, target unit, and value
What you get
Converted value
How to Use
- Select a category (length, weight, temperature, speed, or data storage).
- Choose the source and target units from the dropdowns.
- Enter a value and see the conversion instantly.
Quick Reference: Metric ↔ Imperial
| Metric | Imperial | Formula |
|---|---|---|
| 1 kilometer | 0.621371 miles | km × 0.621371 |
| 1 kilogram | 2.20462 pounds | kg × 2.20462 |
| 0 °Celsius | 32 °Fahrenheit | °F = (°C × 9/5) + 32 |
| 1 liter | 0.264172 US gallons | L × 0.264172 |
| 1 centimeter | 0.393701 inches | cm × 0.393701 |
| 1 meter | 3.28084 feet | m × 3.28084 |
| 1 metric ton | 2204.62 pounds / 1.10231 short tons | t × 1000 × 2.20462 |
| 1 km/h | 0.621371 mph | km/h × 0.621371 |
Why Unit Conversion Gets Tricky
The most expensive unit conversion mistake in history cost NASA $125 million. In 1999, the Mars Climate Orbiter burned up in the Martian atmosphere because one engineering team sent thruster data in pound-force seconds while the receiving software expected newton-seconds. The spacecraft navigated flawlessly for nine months before a unit mismatch destroyed it on arrival. The error was not a calculation bug — both sides computed correctly in their own units. The failure was the assumption that both sides shared the same unit system.
Data storage has its own long-running confusion between SI units (kB = 1,000 bytes) and binary units (KiB = 1,024 bytes). Hard drive manufacturers advertise in SI gigabytes; operating systems report in binary gibibytes. A drive sold as "1 TB" shows as roughly 931 GiB in Windows or macOS — not because either is wrong, but because they are measuring in different bases. The IEC standardized the KiB/MiB/GiB notation in 1998 to resolve this, but the industry has been slow to adopt it uniformly.
Nautical miles and statute miles are another frequent source of confusion in aviation and maritime contexts. A nautical mile (1,852 m exactly) is based on one arcminute of latitude, which makes it naturally compatible with navigation charts. Aircraft altimeters read feet in the US and some European countries, but meters in Russia and China — a detail that matters when descending into an airport with a crew trained on different units.
Pro Tips
- Temperature is the one conversion that is NOT a simple multiplication — it requires both a scale factor and an offset. Double-check any formula before implementing it in code.
- For cooking, 1 US cup = 240 mL (not 250 mL as often approximated) — the difference adds up across multiple cups in baking recipes.
- When working with data sizes in code, always specify whether you mean 1000-based (SI) or 1024-based (IEC) units to avoid the classic 'drive appears smaller than advertised' confusion.
- Knots to km/h: 1 knot = 1.852 km/h exactly (this is a defined value, not a measurement), so the conversion is lossless.
- For quick mental math, 1 kg ≈ 2.2 lbs and 1 mile ≈ 1.6 km are accurate enough for everyday estimates without reaching for a calculator.
Frequently Asked Questions
- How accurate are the conversions?
- Conversions use standard conversion factors and are accurate to full floating-point precision. Results are displayed rounded to 6 significant digits.
- What unit categories are supported?
- Length (m, km, mi, ft, in, cm, mm, yd), weight (kg, g, mg, lb, oz, ton), temperature (C, F, K), speed (m/s, km/h, mph, knots), and data storage (B, KB, MB, GB, TB, PB).
- Does this work offline?
- Yes. All conversions happen in your browser with no server calls, so it works offline once loaded.
- Can I convert between metric and imperial units?
- Yes. The length and weight categories include both metric units (meters, kilograms, grams) and imperial units (feet, inches, miles, pounds, ounces). You can convert freely between any combination of the two systems.
- How does temperature conversion work?
- Temperature conversions between Celsius, Fahrenheit, and Kelvin use the exact mathematical formulas rather than simple multiplication factors. For example, Celsius to Fahrenheit applies the formula F = C x 9/5 + 32, ensuring precise results at every value.
Learn More
Metric vs Imperial: A Complete Unit Conversion Guide with History and Formulas
Explore the history of metric and imperial systems, SI base units, temperature conversion formulas, and the kB vs KiB confusion in data storage.
6 min read