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

Every measurement is a translation. Kilometers into miles. Celsius into Fahrenheit. Kilograms into pounds. The number changes, the physical reality doesn't. But get the translation wrong, and the consequences range from a ruined cake to a crashed spacecraft.

If you've ever stared at a recipe measured in cups and wondered how many milliliters that is, or tried to figure out whether 38 degrees Celsius counts as a fever or a pleasant afternoon, this guide is for you. We'll walk through the most common unit conversions people need every day, give you the actual formulas so you understand what's happening behind the scenes, and point you toward tools that handle the math instantly.

On akousa.net, we maintain over 200 converter tools that handle everything from basic length and weight to obscure engineering and data units. But tools are only useful if you understand what they're doing. So let's build that understanding first.

Length Conversion: Meters, Feet, Miles, and Everything Between#

Length is the conversion most people encounter first. Whether you're reading a European road sign, buying fabric, or checking your height on a medical form in a different country, you need to move between metric and imperial length units constantly.

The Metric Length Ladder#

The metric system makes length conversion trivially easy because everything is a power of 10:

To convert between any two metric length units, you just move the decimal point. 5.2 kilometers is 5,200 meters. 340 centimeters is 3.4 meters. No weird multiplication, no memorization. This is why scientists worldwide use metric exclusively.

Metric to Imperial Length Conversions#

Here's where things get messy. The imperial system has no consistent base. There are 12 inches in a foot, 3 feet in a yard, and 1,760 yards in a mile. None of these numbers relate to each other in any logical way.

The key conversion factors you need:

Quick Mental Math Shortcuts for Length#

You don't always have a converter handy. Here are approximations that work well enough for everyday use:

• Inches to centimeters: Multiply by 2.5 (actual: 2.54). Close enough for estimating.
• Feet to meters: Divide by 3.3. A 6-foot person is roughly 1.82 meters.
• Miles to kilometers: Multiply by 1.6. A 10-mile run is about 16 km.
• Kilometers to miles: Multiply by 0.6. A 5K race is about 3.1 miles.

There's also the Fibonacci trick for miles-to-kilometers: consecutive Fibonacci numbers approximate the conversion. 5 miles is roughly 8 km. 8 miles is roughly 13 km. 13 miles is roughly 21 km. It works because the golden ratio (1.618) is close to the miles-to-km factor (1.609).

Weight and Mass Conversion: Kilograms, Pounds, Ounces, and Grams#

Weight conversion is the second most common daily need, especially for cooking, shipping, and health.

Metric Weight Units#

Imperial Weight Units#

The imperial system uses ounces, pounds, stones (in the UK), and tons. And just to keep things interesting, the US ton (short ton, 2,000 pounds) is different from the UK ton (long ton, 2,240 pounds), which is different from the metric ton (1,000 kilograms, or 2,204.6 pounds).

Key Weight Conversion Formulas#

Quick Mental Math for Weight#

• Pounds to kilograms: Divide by 2.2. A 200-pound person is about 91 kg.
• Kilograms to pounds: Multiply by 2.2. A 75 kg suitcase limit means about 165 pounds.
• Ounces to grams: Multiply by 28. An 8-ounce steak is about 224 grams.

For cooking, memorize this: 1 pound equals approximately 454 grams. Most kitchen scales toggle between grams and ounces, but knowing the conversion saves you when the battery dies.

Temperature Conversion: Celsius, Fahrenheit, and Kelvin#

Temperature is the conversion that trips people up the most because it's not a simple multiplication. Temperature scales have different zero points, so you need both multiplication and addition.

The Three Temperature Scales#

• Celsius (C): Water freezes at 0, boils at 100. Used by essentially every country except the US.
• Fahrenheit (F): Water freezes at 32, boils at 212. Used in the United States and a few Caribbean nations.
• Kelvin (K): Absolute zero is 0 K. Water freezes at 273.15 K. Used in science and engineering. There are no negative Kelvin temperatures.

Temperature Conversion Formulas#

These are the exact formulas:

Celsius to Fahrenheit:

F = (C x 9/5) + 32

Example: 25 C = (25 x 1.8) + 32 = 77 F

Fahrenheit to Celsius:

C = (F - 32) x 5/9

Example: 98.6 F = (98.6 - 32) x 0.5556 = 37 C

Celsius to Kelvin:

K = C + 273.15

Example: 100 C = 373.15 K

Kelvin to Celsius:

C = K - 273.15

Example: 0 K = -273.15 C (absolute zero)

Fahrenheit to Kelvin:

K = (F - 32) x 5/9 + 273.15

Example: 212 F = (212 - 32) x 0.5556 + 273.15 = 373.15 K

Temperature Reference Points Worth Memorizing#

Rather than doing the math every time, memorize these anchor points and estimate from there:

The Quick Estimation Trick for Temperature#

For a rough Celsius-to-Fahrenheit conversion in your head: double the Celsius value and add 30. It's not exact, but it's close enough for deciding whether to bring a jacket.

• 10 C: (10 x 2) + 30 = 50 F (actual: 50 F) -- happens to be exact here
• 20 C: (20 x 2) + 30 = 70 F (actual: 68 F) -- close
• 30 C: (30 x 2) + 30 = 90 F (actual: 86 F) -- a few degrees off but directionally right

For Fahrenheit to Celsius: subtract 30, then divide by 2.

• 80 F: (80 - 30) / 2 = 25 C (actual: 26.7 C) -- reasonable estimate

Volume Conversion: Liters, Gallons, Cups, and Fluid Ounces#

Volume conversion is a nightmare because the imperial system has different definitions depending on which country you're in. A US gallon is not the same as a UK (imperial) gallon. A US fluid ounce is not the same as a UK fluid ounce. And "cups" as a unit of measurement exist almost exclusively in American and Australian cooking.

Metric Volume Units#

Also worth knowing: 1 liter = 1,000 cubic centimeters (cc or cm3). 1 milliliter = 1 cubic centimeter. This relationship between volume and length is one of the metric system's most elegant features.

Key Volume Conversion Formulas#

Cooking Volume Quick Reference#

If you cook with international recipes, pin this to your fridge:

Speed Conversion: km/h, mph, m/s, and Knots#

Speed conversion matters for driving in foreign countries, understanding weather reports, aviation, and maritime navigation.

Key Speed Conversion Formulas#

Speed Reference Points#

The Simple Speed Shortcut#

For km/h to mph, multiply by 0.6 (or equivalently, multiply by 6 and drop the last digit). 100 km/h becomes about 60 mph. 80 km/h becomes about 48 mph. For mph to km/h, multiply by 1.6 -- or add 60% to the number.

Data Storage Conversion: Bits, Bytes, and Beyond#

In an age of cloud storage, streaming, and file transfers, understanding data units is essential. This is also one of the areas where confusion is most common because there are two competing standards: binary (powers of 1,024) and decimal (powers of 1,000).

Binary vs. Decimal: Why Your Hard Drive Seems Smaller Than Advertised#

When you buy a "1 TB" hard drive, the manufacturer means 1,000,000,000,000 bytes (decimal). But your operating system may display storage using binary units, where 1 TB = 1,099,511,627,776 bytes. That's why a "1 TB" drive shows up as roughly 931 GB in your file manager. You didn't lose space. The units just disagree.

To fix this confusion, the IEC introduced binary prefixes (kibibyte, mebibyte, gibibyte), but almost nobody uses them in casual conversation.

Data Unit Conversion Table (Decimal)#

Data Unit Conversion Table (Binary)#

Bits vs. Bytes#

Internet speeds are measured in bits per second (bps), while file sizes are measured in bytes. There are 8 bits in 1 byte. This means:

• A 100 Mbps (megabits per second) connection can theoretically download at 12.5 MB/s (megabytes per second).
• A 1 Gbps connection maxes out at 125 MB/s.
• A 50 MB file on a 100 Mbps connection takes about 4 seconds, not 0.5 seconds.

The formula:

Download time (seconds) = File size (MB) x 8 / Connection speed (Mbps)

This distinction between bits and bytes is the single most common source of confusion in data conversions. ISPs advertise in bits because the numbers look bigger. Your file manager shows bytes because that's what matters for storage. Always check which unit is being used.

Area and Land Measurement Conversion#

Area conversions come up when dealing with real estate, agriculture, and land measurement across different countries.

Key Area Conversion Formulas#

Quick Area References#

• A typical US house: 2,000 sq ft = 186 m2
• A soccer/football pitch: approximately 7,140 m2 = 1.76 acres
• 1 acre = 43,560 square feet (roughly the size of a football field without end zones)
• 1 hectare = 10,000 m2 = 2.47 acres

Pressure, Energy, and Other Specialized Conversions#

Beyond the everyday conversions, there are dozens of specialized unit categories that matter in specific fields.

Pressure#

Tire pressure is the most common everyday use. European cars specify pressure in bar (e.g., 2.3 bar), while US tire gauges read in PSI (e.g., 33 PSI). To convert, multiply bar by 14.5 to get PSI.

Energy#

Note: when nutritionists say "calories," they actually mean kilocalories (kcal). A "2,000-calorie diet" is technically 2,000 kilocalories, or 2,000,000 calories. The food industry just dropped the "kilo" prefix decades ago and never corrected it.

Why an Online Converter Beats Manual Calculation#

You now have the formulas. You could do every conversion by hand. But here's why you shouldn't for anything that matters:

Precision Matters#

The formulas above are rounded. The exact value of 1 inch is 25.4 millimeters, not 25. But 1 mile is 1.609344 kilometers, not 1.6. When you're converting once, rounding is fine. When you're chaining conversions (miles to meters to centimeters), rounding errors compound. A dedicated converter uses the exact conversion factors and handles the precision for you.

Unit Ambiguity#

Is that "ounce" a fluid ounce or a weight ounce? Is that "ton" a short ton, a long ton, or a metric ton? Is that "gallon" a US gallon or an imperial gallon? A well-built converter tool makes you choose explicitly, preventing the kind of ambiguity that crashed the Mars Climate Orbiter.

Speed and Convenience#

You can memorize that 1 kilogram equals 2.20462 pounds. Or you can type "85 kg to lb" into a converter and get 187.39 pounds in under a second. When you're converting a list of 20 ingredients from a European recipe, doing it by hand isn't practical. It's a waste of time that a machine handles perfectly.

Batch and Chain Conversions#

Need to convert 47 different measurements in a spreadsheet? Need to go from miles per hour to meters per second to knots? A converter tool handles chained conversions without you needing to remember intermediate steps or conversion factors.

Using akousa.net's 200+ Converter Tools#

On akousa.net, we've built over 200 dedicated converter tools organized by category. Each converter is designed to do one thing well: take a value in one unit, convert it to another, and show you the result instantly.

The converter categories include:

• Length converters: Kilometers to miles, inches to centimeters, feet to meters, yards to meters, nautical miles, and many more
• Weight converters: Kilograms to pounds, ounces to grams, stones to kg, metric tons to short tons
• Temperature converters: Celsius to Fahrenheit, Fahrenheit to Kelvin, Celsius to Kelvin, and all reverse directions
• Volume converters: Liters to gallons (US and imperial), cups to milliliters, fluid ounces to mL, tablespoons and teaspoons
• Speed converters: km/h to mph, m/s to km/h, knots to mph
• Data storage converters: Bytes to kilobytes, megabytes to gigabytes, bits to bytes, and the full binary/decimal spectrum
• Area converters: Square meters to square feet, acres to hectares, square miles to square kilometers
• Pressure converters: PSI to bar, atmospheres to Pascal, mmHg to kPa
• Energy converters: Calories to joules, BTU to kWh, electronvolts to joules
• Time converters: Hours to minutes, days to seconds, weeks to hours, and Unix timestamp conversions
• Angle converters: Degrees to radians, gradians, and arc-based units
• Frequency converters: Hertz to kilohertz, megahertz, gigahertz

Every converter runs entirely in your browser. No data is sent to a server. No sign-up required. No ads blocking the input field. Just type, convert, and get your answer.

Common Conversion Mistakes and How to Avoid Them#

Confusing Weight and Mass#

Weight and mass are different things. Mass is how much matter an object contains (measured in kilograms). Weight is the force of gravity on that mass (measured in newtons). On Earth, they're proportional, so we use them interchangeably in daily life. But if you're doing physics or engineering calculations, conflating the two will produce wrong answers.

Forgetting Temperature Offsets#

Temperature conversion isn't a simple ratio because Celsius and Fahrenheit have different zero points. You can't just multiply Celsius by 1.8 to get Fahrenheit -- you also need to add 32. Forgetting the offset is the most common temperature conversion error.

Mixing Up US and Imperial Units#

A US pint is 473 mL. An imperial pint is 568 mL. That's a 20% difference. A US gallon is 3.785 liters. An imperial gallon is 4.546 liters. If a British recipe calls for "a pint of cream" and you use an American measuring cup, your dish will be short by almost 100 mL.

Ignoring Significant Figures#

If your bathroom scale reads 82 kg (accurate to the nearest kilogram), converting that to 180.7790 pounds implies a false precision. The converted value should also be rounded to an appropriate number of significant figures: about 181 pounds.

Building Your Conversion Intuition#

The best way to get comfortable with unit conversion is to build a mental library of reference points. Instead of memorizing formulas, memorize anchor values and estimate from there.

Length Anchors#

• Your height in both systems (e.g., 180 cm = 5 ft 11 in)
• A marathon: 42.195 km = 26.2 miles
• A 5K race: 5 km = 3.1 miles

Weight Anchors#

• A liter of water weighs 1 kg (2.2 lb)
• A US nickel weighs 5 grams
• A typical checked baggage limit: 23 kg = 50.7 lb

Temperature Anchors#

• Room temperature: 20-22 C = 68-72 F
• Body temperature: 37 C = 98.6 F
• A hot summer day: 35 C = 95 F
• Freezing: 0 C = 32 F

Volume Anchors#

• A standard water bottle: 500 mL = about 16.9 fl oz
• A US soda can: 355 mL = 12 fl oz
• A liter: slightly more than a US quart (946 mL)

Conclusion#

Unit conversion is one of those skills that seems trivial until you need it and get it wrong. The formulas aren't complicated, but the opportunities for error are everywhere: different zero points in temperature, two competing definitions of a gallon, the bits-versus-bytes trap in data storage, and the sheer number of unit combinations that exist in the world.

For quick estimates, the mental math shortcuts in this guide will serve you well. For anything where precision matters -- cooking, engineering, science, medicine, international shipping -- use a dedicated converter tool. The math is simple enough that a computer handles it perfectly every time, and there's no reason to risk a manual error.

The 200-plus converter tools on akousa.net are built for exactly this purpose: fast, accurate, browser-based conversions with no sign-up and no friction. Whether you need to convert a single temperature reading or process a dozen different unit types, the right tool is a click away.

Measurement systems may never be unified. But at least the conversion doesn't have to be hard.