📏 Length Converter
Convert between metric and imperial length units
📏 Common Length Conversions
How to Convert Units
Unit conversion is the process of changing a measurement from one unit to another while keeping the same quantity. Our free unit converter handles all major unit categories instantly — simply select your units and enter your value.
Metric vs Imperial System
The metric system is used by most countries worldwide and is based on powers of 10 — making conversions within the system simple. The imperial system is primarily used in the United States and includes units like feet, pounds and Fahrenheit. Our converter handles both systems and all conversions between them.
Most Common Unit Conversions
- 1 kilometer = 0.621371 miles
- 1 kilogram = 2.20462 pounds
- 1 meter = 3.28084 feet
- Celsius to Fahrenheit: multiply by 9/5 then add 32
- 1 liter = 0.264172 US gallons
- 1 square meter = 10.7639 square feet
Unit Converter — Length, Weight, Temperature, Volume and More
Unit conversion is one of the most practically useful mathematical skills in everyday life — whether converting temperatures between Celsius and Fahrenheit, weight between kilograms and pounds, distances between miles and kilometres or volumes between litres and gallons. Our unit converter handles all major measurement categories with instant, accurate conversions in both directions between imperial and metric systems.
Length and Distance Conversions — Metric and Imperial
The metric system (used by most of the world) and the imperial system (used primarily in the US) have exact conversion relationships. The fundamental length conversion: 1 inch = 2.54 cm (exactly, by international agreement since 1959). All other length conversions derive from this: 1 foot = 30.48 cm, 1 yard = 91.44 cm, 1 mile = 1.60934 km. For everyday use, helpful mental shortcuts: 1 km is roughly 0.6 miles (more precisely 0.621), 5 miles is roughly 8 km, 100 km is roughly 62 miles. For height conversion, 6 feet = 182.88 cm, 5 feet 10 inches = 177.8 cm. Memorising a few key conversion benchmarks makes mental estimation quick and useful when a calculator is not available. Use our running pace calculator for pace conversions between km and miles and our fuel cost calculator for distance-based fuel cost planning.
| Imperial | Metric | Imperial | Metric |
|---|---|---|---|
| 1 inch | 2.54 cm | 1 foot | 30.48 cm |
| 1 yard | 91.44 cm | 1 mile | 1.6093 km |
| 5 miles | 8.047 km | 100 miles | 160.93 km |
| Marathon (26.22 mi) | 42.195 km | 1 nautical mile | 1.852 km |
Weight and Mass Conversions
The metric unit kilogram (kg) and imperial units pounds (lbs) and ounces (oz) are the most commonly converted weight measurements. The fundamental conversion: 1 kg = 2.20462 lbs (often rounded to 2.2). For quick mental conversion, divide kilograms by 0.45 to get pounds, or multiply pounds by 0.45 for kilograms. Stone (used in the UK for body weight): 1 stone = 14 lbs = 6.35 kg. A person weighing 11 stone = 154 lbs = 69.85 kg. For cooking, 1 ounce = 28.35 grams. 1 US pound = 16 ounces = 453.6 grams. The difference between mass and weight technically matters in physics (mass measures matter; weight measures gravitational force) but in everyday use they are used interchangeably for conversions.
Temperature Conversion — Celsius, Fahrenheit and Kelvin
Celsius (C) and Fahrenheit (F) are the most commonly converted temperature scales. The exact formulas: F = (C × 9/5) + 32 and C = (F − 32) × 5/9. Kelvin (K) is the SI base unit used in science: K = C + 273.15. Key reference temperatures to memorise: 0°C = 32°F (water freezing), 100°C = 212°F (water boiling), 37°C = 98.6°F (normal body temperature), 20°C = 68°F (comfortable room temperature), −40°C = −40°F (the point where both scales are equal). A quick mental approximation for C to F: double the Celsius and add 30 (gives approximate result); exact conversion requires the 9/5 factor.
| Celsius | Fahrenheit | Description |
|---|---|---|
| −10°C | 14°F | Very cold winter |
| 0°C | 32°F | Freezing point of water |
| 20°C | 68°F | Comfortable room temperature |
| 37°C | 98.6°F | Normal body temperature |
| 100°C | 212°F | Boiling point of water |
Volume Conversions — Litres, Gallons and Cooking Measures
Volume conversions are particularly important to get right because US and UK (Imperial) measurements differ significantly — 1 US gallon = 3.785 litres but 1 UK gallon = 4.546 litres, a 20% difference. In cooking, US cups and tablespoons differ from UK measures. 1 US cup = 236.6 ml; 1 UK metric cup = 250 ml. When following recipes from different countries, always verify which cup measurement is being used. For everyday fuel and liquid conversions: 1 litre of water weighs exactly 1 kg at 4°C. Fuel economy units (mpg vs L/100km) require the added step of converting both distance and volume units simultaneously — our fuel cost calculator handles this directly.
Speed and Other Common Conversions
Speed conversion between mph and km/h: 1 mph = 1.60934 km/h. Quick reference: 30 mph = 48.3 km/h, 60 mph = 96.6 km/h, 100 km/h = 62.1 mph. For area: 1 acre = 4,047 m² = 0.4047 hectares. 1 hectare = 10,000 m² = 2.471 acres. For data storage: 1 GB = 1,000 MB (in storage marketing, but technically 1 GiB = 1,024 MiB in computing). For pressure: 1 PSI = 6.895 kPa = 0.06895 bar — important for tire pressure where US uses PSI and most other countries use bar or kPa. Our unit converter provides instant conversions across all these categories and more — enter any value and select the unit type to see conversions displayed immediately.
Why Units Matter — The Cost of Getting Conversions Wrong
Unit conversion errors have caused serious real-world consequences. In 1999, NASA lost the $125 million Mars Climate Orbiter spacecraft because one team used metric units (Newton-seconds) and another used imperial (pound-force-seconds) — the probe entered the Martian atmosphere at the wrong angle and was destroyed. In 1983, Air Canada Flight 143 (the "Gimli Glider") ran out of fuel mid-flight because ground crew calculated fuel load in pounds instead of kilograms — the plane was under-fuelled by more than half. Medical dosing errors caused by unit confusion (mg vs mcg, for example) cause preventable patient harm. These extreme examples illustrate why accurate unit conversion matters — even when the stakes are simply a recipe, a home improvement project or a travel plan, getting units right prevents wasted resources and frustrating mistakes. Our unit converter provides instant, accurate conversions between all major measurement systems so you always have the right number before making any decision that depends on accurate measurement.
Beyond the dramatic examples, everyday unit accuracy matters for cooking (a tablespoon versus a teaspoon is a 3x error), medication dosing, construction material ordering, fuel budgeting and international shopping. Bookmarking our unit converter as your go-to tool for any measurement question ensures you always convert with confidence rather than guessing or using approximate mental shortcuts that introduce cumulative errors in multi-step calculations.