Unit Converter
Convert between length, area, volume, weight, temperature, speed, data, pressure and more – instantly, free, no ads.
Categories
📏 Length Converter
📐 Area Converter
🧊 Volume Converter
⚖️ Weight Converter
🌡️ Temperature Converter
🏎️ Speed Converter
💾 Data Converter
🔧 Pressure Converter
How unit conversion works
Unit conversion is the process of expressing the same physical quantity in a different unit of measurement. Every conversion falls into one of two groups: ratio‑based (most categories) and offset‑based (temperature).
Ratio‑based conversions
For length, weight, area, volume, speed, data and pressure the converter stores each unit as a factor relative to a base unit (metre, kilogram, square metre, litre, m/s, byte, pascal). To convert from unit A to unit B:
result = value × (factorA / factorB)
Because both factors share the same base, the base cancels out and you get the correct ratio every time. For example, to convert 5 miles to kilometres the converter multiplies 5 by the mile‑to‑metre factor and divides by the km‑to‑metre factor, yielding 8.047 km.
Temperature conversions
Temperature scales don't share a common zero — 0 °C, 0 °F and 0 K are all different physical temperatures — so a simple ratio isn't enough. The converter first translates the input to Celsius, then from Celsius to the target scale:
°F = °C × 9/5 + 32 | K = °C + 273.15
Worked examples
| Convert | From | To | Result |
|---|---|---|---|
| 10 | miles | kilometres | 16.093 km |
| 72 | °F | °C | 22.222 °C |
| 100 | kg | lb | 220.462 lb |
| 5 | gallons | litres | 18.927 l |
| 1 | GB | MB | 1,024 MB |
| 30 | psi | bar | 2.068 bar |
Common conversion reference
| Category | Anchor conversion | Use it to remember |
|---|---|---|
| Length | 1 in = 25.4 mm (exact) | Derive feet, yards and miles from inches |
| Area | 1 ft² ≈ 0.0929 m² | 10 ft² is just under 1 m² |
| Volume | 1 gal (US) ≈ 3.785 l | 4 litres is roughly 1 gallon |
| Weight | 1 kg ≈ 2.205 lb | 5 kg ≈ 11 lb |
| Temperature | °F = °C × 1.8 + 32 | Double °C and add 30 for a quick estimate |
| Speed | 1 mph ≈ 1.609 km/h | 50 mph ≈ 80 km/h |
| Data | 1 GB = 1,024 MB | Binary prefix — each step is ×1,024 |
| Pressure | 1 atm = 101.325 kPa ≈ 14.7 psi | Tyre pressure ≈ 2 bar ≈ 30 psi |
Tips for accurate conversions
- Know whether you need precision or an estimate. For cooking, "1 litre ≈ 4 cups" is fine. For engineering, use the exact factor (1 l = 0.264172 gal).
- Watch your significant figures. The converter shows up to 10 significant digits — round to what's appropriate for your use case.
- Temperature is special. Always use the converter for °F ↔ °C ↔ K; a simple ratio will give the wrong answer.
- US vs imperial gallons. This converter uses the US liquid gallon (≈ 3.785 l). The imperial gallon (UK) is larger (≈ 4.546 l).
- Data units are binary. 1 KB = 1,024 B, 1 MB = 1,024 KB — not 1,000. Storage manufacturers sometimes use decimal prefixes (1 MB = 1,000,000 B), which is why a "500 GB" drive shows less in your OS.
Frequently asked questions
What is the difference between metric and imperial?
The metric system (metres, kilograms, litres) is based on powers of ten and is used worldwide. The imperial system (feet, pounds, gallons) is used mainly in the United States and a few other countries. This converter handles both.
How does the converter calculate results?
For most units the converter uses a conversion factor. It multiplies your input by the factor for the source unit, then divides by the factor for the target unit. Temperature conversions use special offset-and-scale formulas because zero is not the same across Celsius, Fahrenheit and Kelvin.
Why is temperature conversion different?
Length, weight and other quantities share the same zero point — zero metres equals zero feet. Temperature scales have different zero points (0 °C ≠ 0 °F ≠ 0 K), so converting requires both a multiplication and an addition, not just a single ratio.
Are the conversions exact?
Most conversions use internationally agreed exact definitions (e.g. 1 inch = 25.4 mm exactly). Results are shown to six decimal places; for most practical purposes you can round to two or three.
What is the best way to remember common conversions?
Learn a few anchor points: 1 inch ≈ 25.4 mm, 1 foot ≈ 0.305 m, 1 mile ≈ 1.609 km, 1 kg ≈ 2.205 lb, 1 litre ≈ 0.264 gal. From these you can derive the rest.