Unit Converter Online — Convert Length, Weight, Temperature & More

The world runs on two major measurement systems — the metric system used by most countries and the imperial system primarily used in the United States — and they almost never agree. A road sign in the UK shows miles; your GPS speaks kilometres. A recipe calls for ounces; your kitchen scale reads grams. A weather app switches between Celsius and Fahrenheit. Unit conversion is a constant friction point in daily life, science, and international commerce.

This guide explains the most important unit conversions you will encounter, gives you the formulas to calculate them, and points you to our free online converter tools for instant results. Whether you are a student, traveller, engineer, or cook, this is your complete unit conversion reference.

Metric vs Imperial: The Basics

The metric system (officially the International System of Units, or SI) is based on powers of ten. Each unit is 10×, 100×, or 1000× larger or smaller than the adjacent unit. This makes metric arithmetic straightforward — converting 1.5 km to metres is simply 1500 m (multiply by 1000). The metric system is used by 195+ countries and is the standard in all scientific and most commercial contexts worldwide.

The imperial system uses historically derived units with non-decimal relationships: 12 inches in a foot, 3 feet in a yard, 1,760 yards in a mile. Weight uses ounces, pounds, and tons with their own non-decimal factors. Only three countries — the United States, Liberia, and Myanmar — continue to use imperial as their primary system of measurement.

Even within the imperial system there are differences between the US and UK versions. A US gallon is 3.785 litres; a UK gallon is 4.546 litres. A US ton (short ton) is 2,000 lbs; a UK ton (long ton) is 2,240 lbs. These differences cause real errors in international trade and manufacturing, making unit conversion accuracy crucial.

Length Conversions

Length is the most commonly converted unit in everyday life. Here are the key conversion factors:

From	To	Multiply By
Kilometres (km)	Miles	0.621371
Miles	Kilometres	1.60934
Metres (m)	Feet	3.28084
Feet	Metres	0.3048
Centimetres (cm)	Inches	0.393701
Inches	Centimetres	2.54
Metres	Yards	1.09361
Yards	Metres	0.9144

Quick reference: 1 km ≈ 0.62 miles (or roughly 5/8 of a mile). For travel, a useful approximation is: multiply km by 0.6 to get miles (slight underestimate, easy to compute). Use our length converter for precise results across all units.

Weight Conversions

Weight conversions frequently come up in cooking, fitness, shopping (especially when ordering internationally), and medicine. Key conversions:

From	To	Multiply By
Kilograms (kg)	Pounds (lbs)	2.20462
Pounds (lbs)	Kilograms	0.453592
Grams (g)	Ounces (oz)	0.035274
Ounces (oz)	Grams	28.3495
Kilograms	Stone	0.157473
Stone	Kilograms	6.35029

Memory aid: 1 kg ≈ 2.2 lbs. So a 70 kg person weighs approximately 70 × 2.2 = 154 lbs. Use our weight converter for all unit combinations.

Temperature Conversions

Temperature is unique among unit conversions because the scales do not share the same zero point — you cannot simply multiply. The three most common temperature scales are Celsius (°C), Fahrenheit (°F), and Kelvin (K).

From	To	Formula
Celsius	Fahrenheit	°F = (°C × 9/5) + 32
Fahrenheit	Celsius	°C = (°F − 32) × 5/9
Celsius	Kelvin	K = °C + 273.15
Kelvin	Celsius	°C = K − 273.15

Memory points: Water freezes at 0°C / 32°F / 273.15K. Water boils at 100°C / 212°F / 373.15K. Normal body temperature is 37°C / 98.6°F. Our temperature converter handles all four scales including Rankine.

Speed Conversions

Speed conversions matter for driving, aviation, sailing, and weather forecasting. Key conversions:

• 1 km/h = 0.621371 mph — multiply by 0.621 for quick estimates
• 1 mph = 1.60934 km/h
• 1 m/s = 3.6 km/h = 2.237 mph
• 1 knot = 1.852 km/h (used in aviation and nautical navigation)
• 1 Mach ≈ 1235 km/h at sea level (varies with altitude and temperature)

Highway speed limits in India are typically 100–120 km/h on expressways. In the US, that translates to approximately 62–75 mph. Use our speed converter for precise conversions including Mach numbers.

Area Conversions

Area conversions are essential in real estate, agriculture, and construction. In India, land area is commonly measured in square feet, square metres, cents, guntha, and bigha — units that vary by state. International units include square metres, acres, and hectares.

From	To	Multiply By
Square metres (m²)	Square feet (sq ft)	10.7639
Square feet	Square metres	0.0929
Hectares (ha)	Acres	2.47105
Acres	Hectares	0.404686
Square kilometres	Square miles	0.386102

Use our area converter for Indian land units like cents, guntha, and bigha alongside international standards.

Data Storage Conversions

As digital storage grows from gigabytes to terabytes to petabytes, understanding data unit conversions is increasingly relevant. The key hierarchy:

• 1 Byte = 8 bits
• 1 Kilobyte (KB) = 1,024 bytes (binary) or 1,000 bytes (decimal/SI)
• 1 Megabyte (MB) = 1,024 KB = 1,048,576 bytes
• 1 Gigabyte (GB) = 1,024 MB
• 1 Terabyte (TB) = 1,024 GB
• 1 Petabyte (PB) = 1,024 TB

Hard drive manufacturers use decimal (1,000-based) definitions, which is why a "1 TB" hard drive shows approximately 931 GB in Windows (which uses binary definitions). This discrepancy confuses many users. Use our data storage converter to convert accurately between both conventions.

Unit Conversion for Travellers

Travelling internationally involves a constant stream of unit conversion challenges. Here is a practical travel conversion cheat sheet:

• Distance: 1 mile = 1.6 km. A "5 mile" hike is about 8 km.
• Temperature: 30°C = 86°F (hot summer day). 0°C = 32°F (freezing). Add 30 to °C and halve it for a rough °F estimate.
• Weight (luggage): 20 kg baggage limit = 44 lbs.
• Fuel efficiency: UK MPG ≠ US MPG. 40 UK mpg = 33.3 US mpg because UK gallons are larger.
• Clothing sizes: US size 8 shoe = UK size 7 = EU size 41. Size conversions vary by brand.
• Food quantities: 1 cup (US) = 240 mL. 1 US fluid ounce = 29.57 mL.

Unit Conversion in Science & Engineering

Precision matters even more in science and engineering. The Mars Climate Orbiter was lost in 1999 because one team used metric units and another used imperial — a $327 million lesson in unit conversion importance. In science, all calculations should use SI units as the base, converting input data first before performing calculations.

Common science conversions include: energy (joules, calories, electronvolts, BTUs); pressure (pascals, bar, atmospheres, psi); frequency (Hz, kHz, MHz, GHz); and force (newtons, kilogram-force, pounds-force). Our suite of converters includes energy, pressure, and speed converters for these more technical use cases.

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