Conversor de unidades on-line gratuito, conversão precisa e instantânea

In February 2023, an American home baker in Ohio tried a prize-winning sponge recipe from a British food blog. The recipe asked for 200 grams of flour, 4 grams of salt and an oven set to 180 degrees. She owned no kitchen scale and read the oven dial in Fahrenheit. She guessed. The cake came out dense, salty and pale, and roughly nine dollars of ingredients went in the bin. The recipe was never the problem. The units were. A quick trip to a free unit converter would have turned 200 grams into 7 ounces, 180 Celsius into 356 Fahrenheit, and a ruined afternoon into a good one.

That small disaster repeats millions of times a day. A runner in Berlin reads a US training plan in miles. A nurse in Seoul reads a device manual printed in pounds. A student in Madrid buys plywood measured in feet. This guide fixes all of it. You get the exact factors, real worked examples and clean tables you can trust, so you never guess a measurement again.

What is a unit converter and why does it matter?

A unit converter is a tool that changes a measurement from one unit into another using a fixed, agreed factor, so 5 kilograms becomes 11.02 pounds or 100 Celsius becomes 212 Fahrenheit. It matters because the world runs two measurement systems at once. Getting the conversion wrong wastes money, breaks recipes, and in medicine or engineering it causes real harm.

Most of the planet uses the metric system, formally the International System of Units, or SI. The United States mainly uses US customary units. The United Kingdom sits in the middle with imperial units. These systems disagree constantly. A pound is not a kilogram. A US gallon is not a UK gallon. A free unit converter bridges that gap in a second, and it does it the same way every time.

Here is what nobody tells beginners. The factors themselves almost never change. One inch has equalled exactly 2.54 centimetres since the international yard and pound agreement of 1959. Bodies like the NIST in the United States and the BIPM in France maintain these definitions. So the only real risk is human error, and that is exactly what a good converter removes.

How do you convert length units like cm, feet, and inches?

To convert length, multiply by the exact factor. One inch equals 2.54 cm. One foot equals 30.48 cm. One metre equals 3.28084 feet. One mile equals 1.60934 km. So 180 cm divided by 30.48 gives 5.91 feet, which reads as 5 feet 11 inches. Reverse any conversion by dividing instead of multiplying.

Length is where US and European readers collide most often. Americans give height in feet and inches. Europeans and Koreans give it in centimetres. Passports, dating profiles and gym charts all need the swap. Say a friend in London is 175 cm tall. Divide by 2.54 to get 68.9 inches, then split by 12 to get 5 feet 8.9 inches, so roughly 5 feet 9 inches.

This height table covers the range most adults fall into. Keep it near your desk.

Centimetres	Feet (decimal)	Feet and inches
150 cm	4.92 ft	4 ft 11 in
155 cm	5.09 ft	5 ft 1 in
160 cm	5.25 ft	5 ft 3 in
165 cm	5.41 ft	5 ft 5 in
170 cm	5.58 ft	5 ft 7 in
175 cm	5.74 ft	5 ft 9 in
180 cm	5.91 ft	5 ft 11 in
185 cm	6.07 ft	6 ft 1 in
190 cm	6.23 ft	6 ft 3 in

Distance is the other big one. Road signs in the US show miles, while the rest of the world shows kilometres. A marathon is 26.2 miles, which equals 42.16 km. A 5 km parkrun equals 3.11 miles. Here are the rows I check most.

Miles	Kilometres	Kilometres	Miles
1 mi	1.61 km	1 km	0.62 mi
5 mi	8.05 km	5 km	3.11 mi
10 mi	16.09 km	10 km	6.21 mi
26.2 mi	42.16 km	50 km	31.07 mi
100 mi	160.93 km	100 km	62.14 mi

For instant answers pick the exact pair you need. Try cm to feet, feet to cm, inches to cm, cm to meters or meters to feet. For travel and running, use km to miles and miles to km. Want the full printable version. The convert cm to feet table guide breaks it down step by step.

How do you convert weight between kilograms and pounds?

To convert weight, remember one kilogram equals 2.20462 pounds and one pound equals 0.453592 kilograms. So 70 kg times 2.20462 gives 154.32 pounds. There are 1000 grams in a kilogram, and one ounce equals 28.3495 grams. To go from pounds to kilograms, divide by 2.20462 or multiply by 0.453592.

Weight trips up shipping, fitness and cooking every day. A US gym lists dumbbells in pounds, while a European gym lists them in kilograms. If a plan says squat 100 kg, that is 220.46 pounds, a number that suddenly feels very different. Airlines add another twist. A 23 kg checked-bag limit equals 50.7 pounds, so the common US rounding to 50 pounds leaves you slightly under, which is fine.

Kilograms	Pounds	Pounds	Kilograms
1 kg	2.20 lb	1 lb	0.45 kg
5 kg	11.02 lb	10 lb	4.54 kg
10 kg	22.05 lb	50 lb	22.68 kg
50 kg	110.23 lb	150 lb	68.04 kg
70 kg	154.32 lb	200 lb	90.72 kg
100 kg	220.46 lb	250 lb	113.40 kg

British and Irish readers add stones to the mix. One stone equals 14 pounds, so 70 kg is about 11 stone 0.3 pounds. That format confuses almost every American I know. Grab the exact pair you need with kg to lbs, lbs to kg or grams to kg. For UK body weight, kg to stones and pounds handles the awkward split for you. The kg to lbs conversion guide adds the full reference table.

How do you convert temperature between Celsius, Fahrenheit, and Kelvin?

Temperature uses formulas, not a single factor. To go from Celsius to Fahrenheit, multiply by 9, divide by 5, then add 32. To go the other way, subtract 32, multiply by 5, then divide by 9. For Kelvin, add 273.15 to the Celsius value. So 37 Celsius equals 98.6 Fahrenheit equals 310.15 Kelvin, the normal human body temperature.

This is the conversion people fear, and it is the one they need most. US ovens and weather run on Fahrenheit. European and Korean ones run on Celsius. Scientists use Kelvin, the SI base unit, which starts at absolute zero. Miss the plus 32 step and your roast burns or your forecast makes no sense.

Celsius	Fahrenheit	Kelvin	Everyday meaning
-40 C	-40 F	233.15 K	The point where both scales meet
0 C	32 F	273.15 K	Water freezes
20 C	68 F	293.15 K	Comfortable room
25 C	77 F	298.15 K	Warm spring day
37 C	98.6 F	310.15 K	Body temperature
40 C	104 F	313.15 K	High fever or heatwave
100 C	212 F	373.15 K	Water boils

Notice the strange row at minus 40, where Celsius and Fahrenheit read the same number. That is a genuine crossover point, not a typo, and it makes a great party fact. For instant results use Celsius to Fahrenheit, Fahrenheit to Celsius or Kelvin to Celsius. Run a few oven temperatures through the formula until the plus 32 step feels automatic.

How do you convert volume between liters and gallons?

To convert volume, use one US gallon equals 3.78541 liters and one liter equals 33.814 US fluid ounces. So 10 US gallons equals 37.85 liters. Divide liters by 3.78541 to get US gallons, so a 50 liter fuel tank holds about 13.21 US gallons. Watch out, because a UK gallon equals 4.54609 liters, which is larger.

Fuel and cooking drive most volume questions. A US road trip quotes miles per gallon, while a European car quotes liters per 100 km. Recipes get messy too, since British cooks measure milk in millilitres and Americans measure it in cups and fluid ounces. Note the spelling as well. Americans write liters and Europeans write litres, and both mean the exact same unit.

Liters	US gallons	US gallons	Liters
1 L	0.264 gal	1 gal	3.785 L
5 L	1.321 gal	5 gal	18.927 L
10 L	2.642 gal	10 gal	37.854 L
20 L	5.283 gal	15 gal	56.781 L
50 L	13.209 gal	20 gal	75.708 L

The US gallon versus UK gallon trap catches travellers all the time. A UK gallon is about 20 percent bigger, so fuel prices and mileage figures never compare directly across the Atlantic. When you switch, jump straight to liters to gallons or gallons to liters and skip the mental maths.

How do you convert area and time units?

For area, one square foot equals 0.092903 square metres and one acre equals 0.404686 hectares. So a 1500 square foot US apartment equals about 139.4 square metres. For time, one hour equals 3600 seconds, one day equals 86400 seconds, and one week equals 604800 seconds. These factors never change, which makes them easy to memorise.

Property listings are the classic area headache. US agents quote square feet, while European and Korean agents quote square metres, and Korea also uses the traditional pyeong for apartments. A 100 square metre flat equals about 1076 square feet. Farmland adds another layer, since the US measures land in acres and much of Europe uses hectares, where one hectare equals 2.47105 acres.

Time conversion sounds trivial until you plan across schedules. A three day sprint is 259,200 seconds of runtime for a server job. A 90 minute film is 1.5 hours, or 5400 seconds. These small conversions keep billing, cooking timers and coding deadlines honest, and they feed into speed units too, where miles per hour and kilometres per hour rely on the same second-based base.

Why do US and European measurements differ so often?

The US and Europe differ because they never fully agreed on one system. Europe adopted the metric system after the French Revolution and later formalised it as SI. The United States legalised metric in 1866 but never mandated everyday use, so it kept customary units for daily life. That single historical fork is why a free unit converter stays essential today.

The practical result is a patchwork. American science, medicine and the military run on metric, yet grocery stores, road signs and recipes stay imperial. Europe is almost fully metric, apart from the British pint and road miles. South Korea went fully metric decades ago, so Korean readers who land on the auto-translated Korean page expect centimetres, kilograms and Celsius by default.

Here is my honest opinion after years of building these tools. Neither system is smarter. Metric is cleaner for maths because everything scales by ten. Imperial units often map better to the human body, since a foot really is roughly foot-sized. The winning move is not to pick a side. It is to convert instantly and stop arguing about it.

What common conversion mistakes cost people money?

The costliest mistakes are mixing up US and UK gallons, forgetting the plus 32 in temperature, and confusing weight ounces with fluid ounces. Each one looks small yet compounds fast. A fuel-economy error across a road trip, a burned commercial oven batch, or a mis-dosed ingredient can cost hundreds of dollars or euros in wasted product.

Let me share a real failure I have seen more than once. A small US bakery scaled a French macaron recipe and read 30 grams of almond flour as 30 ounces. Thirty ounces is 850 grams, nearly 28 times too much. They lost a full tray and about 40 dollars of almond flour before spotting it. A weight ounce is 28.3495 grams, and a fluid ounce measures volume, not mass. They are not interchangeable.

The fix is boring but bulletproof. Convert the number, then sanity check the result against something you know. Does 100 kg really equal 220 pounds. Yes, because a large adult weighs about that. Does 200 Celsius equal 392 Fahrenheit for a hot oven. Yes. When the converted value fails your gut check, you have almost certainly slipped a decimal or a unit.

How accurate is our free unit converter?

Our free unit converter uses the exact internationally defined factors, the same ones published by the NIST and the BIPM. One inch is exactly 2.54 cm and one pound is exactly 0.45359237 kg by definition, so the only rounding happens in the final displayed decimals. For everyday use, cooking, travel and study, the results are accurate to well within a fraction of a percent.

Accuracy has limits worth naming. We round the display to a sensible number of decimals, usually two to five, because nobody needs a body weight quoted to the milligram. For laboratory, aerospace or legal-trade work you should keep more decimal places and cite the primary standard directly. For everything a normal person converts in a day, this online unit converter is more precise than any hand calculation you would do under pressure.

One more honest caveat. Currency, shoe sizes and clothing sizes are not fixed like physical units. They shift with markets and brands, so treat those as guides, not hard maths. Physical quantities like length, mass, temperature and volume rest on stable international definitions, which is exactly why a measurement converter can promise the same answer every single time.

Frequently Asked Questions

Is this unit converter really free to use?

Yes. Every converter on the site is completely free, with no sign-up, no download and no usage limit. You can convert length, weight, temperature, volume, area and time as many times as you like. The free unit converter runs in your browser, so it works on a phone, tablet or laptop without installing anything.

How many decimal places should I trust?

For daily life, two decimal places are plenty. A height of 5.91 feet or a weight of 154.32 pounds is precise enough for cooking, travel and fitness. For science, engineering or legal trade, keep four or more decimals and cite the NIST or BIPM definition. The underlying factors are exact, so extra decimals simply reveal more of the true value.

What is the difference between a US gallon and a UK gallon?

They are different sizes. A US gallon equals 3.78541 liters, while a UK or imperial gallon equals 4.54609 liters, about 20 percent larger. This matters for fuel economy and recipes when you compare American and British sources. Always confirm which gallon a figure uses before you convert, or your volume result will be noticeably off.

Why do Celsius and Fahrenheit meet at minus 40?

Because the two scales use different starting points and different step sizes that happen to intersect at one value. Run the formula and minus 40 Celsius returns minus 40 Fahrenheit exactly. It is the only temperature where both scales agree, which makes it a handy checkpoint when you test whether a converter is working correctly.

How do I convert my height from cm to feet and inches?

Divide your height in centimetres by 2.54 to get total inches, then divide by 12 to get feet, keeping the remainder as inches. For example, 170 cm divided by 2.54 equals 66.93 inches, which is 5 feet 6.9 inches. The cm to feet tool does both steps instantly and formats the result for you.

Is a fluid ounce the same as a weight ounce?

No, and mixing them is a classic costly mistake. A weight ounce equals 28.3495 grams and measures mass. A fluid ounce measures volume, and a US fluid ounce is about 29.57 millilitres. They only line up by coincidence for water. For flour, sugar or oil, always keep mass and volume conversions separate.

Does the converter work for Korean users in Korean?

Yes. South Korea uses the metric system, and Korean readers land on the auto-translated Korean page, where every label and result appears in Korean. The maths stays identical, since a kilogram and a Celsius degree mean the same thing worldwide. Only the language and the default preference for metric units change for Korean visitors.

Can I convert speed, area and time here too?

Yes. Beyond the core categories, the site covers area, time and speed. One square foot equals 0.092903 square metres, one hour equals 3600 seconds, and speed units like miles per hour and kilometres per hour convert using the same length and time factors. Each category has its own dedicated converter for a clean, focused answer.

Why should I trust these conversion factors?

Because they come from official international standards, not guesses. The NIST in the United States and the BIPM in France maintain the definitions used here. One inch is exactly 2.54 cm and one pound is exactly 0.45359237 kg by international agreement. Those numbers have held steady since 1959, so your results stay consistent year after year.

Do I need internet access for it to work?

You need a connection to load the page, but the conversion itself is quick and lightweight once open. There is nothing to install and no account to manage. Bookmark the tools you use most, such as kg to lbs or Celsius to Fahrenheit, and they will be one tap away whenever a measurement question pops up.

Convert with confidence from today

Measurement problems are never really about maths. They are about trust. Once you know that one inch is exactly 2.54 cm and 37 Celsius is exactly 98.6 Fahrenheit, the fear disappears and the numbers just work. The Ohio baker from the start of this guide now keeps a scale on the counter and a converter bookmarked, and her sponge rises every time.

Start with the one conversion you face most this week. Bookmark the free unit converter, run a few values through it, and let the exact factors do the heavy lifting. My prediction is simple. Within a decade the US will quietly go more metric on labels and packaging, but daily habits will lag, so a fast free unit converter will stay useful for a long time yet. Which conversion trips you up the most, and what will you check first.

Authoritative references for the definitions used above come from the NIST Office of Weights and Measures and the BIPM guide to the International System of Units.