Last updated: May 2026
Convert between metric and imperial units for length, weight, temperature, volume, speed, and area. Works both directions — type in either field.
Convert between metric (mm, cm, m, km) and imperial (in, ft, yd, mi)
Convert between kg, g, lb, oz, stone, and more
Convert between Celsius, Fahrenheit, and Kelvin
Convert between liters, ml, gallons, cups, fl oz, and more
Convert between km/h, m/s, mph, knots, and more
Convert between m², km², hectares, sq ft, sq mi, acres, and more
Quick Reference — Most Common Conversions
| Metric | Imperial |
|---|---|
| 1 cm | 0.394 in |
| 1 m | 3.281 ft / 1.094 yd |
| 1 km | 0.621 mi |
| 1 kg | 2.205 lb |
| 1 kg | 0.157 st |
| 1 g | 0.035 oz |
| 1 metric ton | 2,204.6 lb |
| Metric | Imperial / US |
|---|---|
| 1 liter | 0.264 gal / 33.8 fl oz |
| 1 liter | 2.113 pt / 4.227 cups |
| 1 ml | 0.202 tsp / 0.068 tbsp |
| 1 km/h | 0.621 mph |
| 1 m/s | 3.281 fps |
| 1 hectare | 2.471 acres |
| 1 m² | 10.764 ft² |
Metric system (SI): Used by ~95% of the world. Based on powers of 10 — every unit is 10× the next smaller unit. Length: millimeter → centimeter → meter → kilometer. Weight: milligram → gram → kilogram → metric ton.
Imperial system: Used primarily in the United States, and partially in the UK and Canada. Based on historical conventions without a consistent multiplier — 12 inches in a foot, 3 feet in a yard, 1,760 yards in a mile, 16 ounces in a pound, 14 pounds in a stone.
Why both matter: Science and medicine use metric globally. US recipes, road signs, and product specs use imperial. Most international travel, shipping, and trade requires both.
Temperature note: Fahrenheit and Celsius cross at −40° (−40°C = −40°F). The formula: °F = (°C × 9/5) + 32. Water freezes at 0°C / 32°F and boils at 100°C / 212°F at sea level.
What are the most commonly converted units in everyday life?
The top five: (1) Kilometers to miles (travel, exercise), (2) Celsius to Fahrenheit (weather, cooking), (3) Kilograms to pounds (body weight, shipping), (4) Liters to gallons (fuel, recipes), and (5) Centimeters to inches (clothing, furniture). These five conversions cover the vast majority of international unit mismatches that come up in daily life.
Why doesn't the US use the metric system?
The US nearly switched in the 1970s — the Metric Conversion Act of 1975 was signed into law, but participation was voluntary. Consumer habits didn't shift, and political momentum faded. Today, US science, medicine, pharmaceuticals, and international trade all use metric. Everyday consumer life (road signs, food packaging, personal height and weight) still uses imperial. The cost and inertia of switching everything over is the primary barrier at this point.
Which unit conversions are easy to do in your head?
Good mental math shortcuts: miles to km — multiply by 1.6 (or use the Fibonacci sequence: 1, 1, 2, 3, 5, 8, 13... miles and km alternate). kg to lb — multiply by 2.2. Celsius to Fahrenheit — double and add 30 (approximate). Inches to cm — multiply by 2.5. Gallons to liters — multiply by 3.8. These are close enough for everyday estimates.
How do international clothing sizes convert?
Clothing sizes don't convert cleanly because they're not standardized internationally — a US size 8 dress is roughly a UK size 12, EU size 38, and Italian size 42, but sizing varies by brand and country. For the most reliable result: convert the actual body measurements (chest, waist, hips in cm or inches) to the target country's size chart, rather than trying to convert the size number directly.
What's the hardest unit conversion to get right?
Volume is the most error-prone, specifically because there are multiple competing "gallons" (US, UK, dry gallon) and "fluid ounces" (US = 29.57 ml, UK = 28.41 ml). Temperature conversions are also commonly done wrong because people forget to handle the offset — you can't just multiply, you also have to shift. Area and volume conversions trip people up because you have to square or cube the linear factor, not just multiply by it once.