Convert common units of length, weight, temperature, volume, area, and speed with transparent formulas and easy-to-read results.
Choose a category, pick your units, and enter a value for an instant conversion.
A unit converter changes a measurement from one unit into another while preserving the same physical quantity. For example, five feet and 152.4 centimeters describe the same length. The number changes because the unit changes.
The basic idea is: original value times conversion factor equals converted value. If a conversion factor is exact, the mathematical relationship is exact even when the displayed result is rounded.
For example, 1 inch equals exactly 2.54 centimeters. So 10 inches times 2.54 equals 25.4 centimeters. CalculateThisWay keeps greater internal precision and rounds only the displayed answer when needed.
The National Institute of Standards and Technology publishes official conversion factors between many U.S. customary and SI units. The International System of Units itself is maintained internationally by the Bureau International des Poids et Mesures.
Millimeters, centimeters, meters, and kilometers each move by a power of ten, which is what makes metric conversions straightforward.
| Unit | Equal To |
|---|---|
| 1 centimeter | 10 millimeters |
| 1 meter | 100 centimeters |
| 1 kilometer | 1,000 meters |
The metric system used for modern science and measurement is centered on the International System of Units, commonly abbreviated SI. SI uses units such as the meter for length, the kilogram for mass, the second for time, and the kelvin for thermodynamic temperature.
It also uses decimal prefixes. For example, 1 kilometer equals 1,000 meters, 1 centimeter equals 0.01 meter, and 1 millimeter equals 0.001 meter. This decimal structure makes many metric conversions straightforward. Moving from meters to centimeters means multiplying by 100. Moving from centimeters to meters means dividing by 100.
The conversion between inches and centimeters is exact: 1 inch equals 2.54 centimeters. So 6 inches times 2.54 equals 15.24 cm, 12 inches times 2.54 equals 30.48 cm, and 60 inches times 2.54 equals 152.4 cm.
This exact relationship is also the foundation for converting feet to centimeters, because one foot contains exactly 12 inches.
One foot is twelve inches, and twelve inches is exactly 30.48 centimeters.
| Unit | Value |
|---|---|
| 1 foot | 12 inches |
| 12 inches | 30.48 centimeters |
First convert feet into inches. Then multiply by 2.54. Example: 5 feet. 5 times 12 equals 60 inches. 60 times 2.54 equals 152.4 centimeters.
For a height such as 5 feet 4 inches, convert the feet first: 5 times 12 equals 60. Add the remaining four inches: 64 inches. Then 64 times 2.54 equals 162.56 cm.
For a height-focused input that accepts feet and inches separately, you can also use the CalculateThisWay Height Calculator.
To convert centimeters back into feet and inches: centimeters divided by 2.54 equals total inches. Then divide the total inches by 12.
Example: 170 cm divided by 2.54 is about 66.93 inches. 66.93 inches contains 5 full feet with about 6.93 inches remaining. So 170 cm is about 5 ft 6.9 in.
Do not round the total inches before calculating the remainder, because early rounding can change the displayed inch value.
The international pound is defined exactly as 0.45359237 kilogram. So 150 lb times 0.45359237 is about 68.04 kg. The reverse calculation is kilograms divided by 0.45359237, or equivalently multiply by approximately 2.20462.
In everyday conversation people call this a weight conversion. Technically, pounds and kilograms in this context are being used as units of mass. For an everyday converter, "Weight / Mass" is the clearest label.
Suppose 70 kg. Using the conversion, 70 divided by 0.45359237 is about 154.32 lb. The calculator keeps greater precision internally but can display a result such as 154.3 lb unless you request more decimal places.
Temperature conversion is different from most length or mass conversion. Celsius and Fahrenheit do not have the same zero point.
20°C. 20 × 9/5 = 36. 36 + 32 = 68°F. So 20°C = 68°F.
Reverse the process.
Example: 68°F. 68 − 32 = 36. 36 × 5/9 = 20°C.
Water freezes at 0°C, 32°F, and 273.15 K, and boils at 100°C, 212°F, and 373.15 K at standard atmospheric pressure.
| Reference Point | Celsius | Fahrenheit | Kelvin |
|---|---|---|---|
| Water freezes | 0°C | 32°F | 273.15 K |
| Water boils (standard atmospheric pressure) | 100°C | 212°F | 373.15 K |
The Celsius degree and kelvin have the same size increment, but different zero points.
So 0°C = 273.15 K and 100°C = 373.15 K. Kelvin values cannot go below zero because zero kelvin represents absolute zero. A valid converter should prevent impossible values below absolute zero, which is why this calculator rejects Kelvin below zero, Celsius below -273.15, and Fahrenheit below about -459.67.
Volume requires special care because "gallon" does not mean exactly the same thing everywhere. A U.S. liquid gallon is different from an Imperial gallon. That is why this calculator explicitly labels US gallon and Imperial gallon instead of displaying one ambiguous "gallon" option. The same issue can apply to pints, fluid ounces, and cups depending on the measurement system.
A US gallon equals 3.785411784 liters. An Imperial gallon equals 4.54609 liters. They are not interchangeable.
| Unit | Liters |
|---|---|
| US gallon | 3.785411784 L |
| Imperial gallon | 4.54609 L |
When following a recipe, check whether the source uses U.S., Imperial, or metric volume units before converting.
A U.S. cup and a metric cup are not identical. If a calculator includes both, they must be separately labeled. This is especially important for cooking, because converting a recipe using the wrong cup definition can noticeably change an ingredient quantity. For scientific and technical measurement, liters and milliliters provide a clearer, internationally standardized reference.
Area conversions require squaring the length factor. One international foot equals 0.3048 meters. But one square foot is not 0.3048 square meters. Instead, 1 ft² = 0.3048 m × 0.3048 m = 0.09290304 m².
1 ft × 1 ft = 1 ft² = 0.09290304 m². The area factor is the length factor squared, not the plain length factor.
| Quantity | Factor |
|---|---|
| 1 foot to meters (length) | 0.3048 |
| 1 square foot to square meters (area) | 0.09290304 |
This distinction matters for flooring, rooms, property areas, and construction materials. If you need to calculate an area from room dimensions first, use the CalculateThisWay Square Footage Calculator.
Acres are commonly used for land area in the United States and some other countries. Hectares are commonly used in metric land measurement. One hectare equals 10,000 square meters, and one acre equals 4,046.8564224 square meters, or exactly 43,560 square feet. A converter makes it easier to move between acres, hectares, square feet, square meters, and square kilometers without repeatedly rebuilding the formulas manually.
One international mile equals exactly 1.609344 kilometers. Therefore, 1 mph equals 1.609344 km/h. Example: 60 mph times 1.609344 equals 96.56064 km/h. Displayed sensibly, 60 mph is about 96.56 km/h.
Reverse the conversion: km/h divided by 1.609344. Example: 100 km/h divided by 1.609344 is about 62.14 mph. If you need to calculate speed from distance and time rather than simply convert speed units, use the CalculateThisWay Speed Calculator.
A knot is one nautical mile per hour. It is commonly used in aviation, marine navigation, and weather reporting. A nautical mile differs from an ordinary statute mile, which means 1 knot is not the same as 1 mph. The converter uses the proper nautical-mile relationship rather than treating the units as interchangeable.
Some conversion relationships are exact. Others may be displayed using a rounded conversion factor or result. Even when the underlying conversion is exact, the answer shown on screen may need rounding for readability. For example, 60 mph times 1.609344 equals 96.56064 km/h. Showing 96.56 km/h does not change the actual mathematical relationship. It simply limits the number of displayed decimal places. The calculator never repeatedly rounds an intermediate number, because those small errors can accumulate.
Possible reasons include different rounding settings, older conversion factors, confusing U.S. and Imperial units, using the U.S. survey foot instead of the international foot, rounding before finishing the calculation, and displaying fewer decimal places. If two results differ only in the last decimal place, rounding may be the reason. If they differ substantially, check whether both tools are using the same unit definition.
A general Unit Converter is best when you already know the measurement and simply need another unit. Examples: inches to centimeters, pounds to kilograms, Fahrenheit to Celsius, miles per hour to kilometers per hour.
Use a specialized CalculateThisWay calculator when you need to solve a larger problem. The Height Calculator is designed for feet, inches, and centimeters. The Square Footage Calculator calculates area from dimensions. The Speed Calculator solves speed, distance, or time. The Gas Mileage Calculator handles MPG and fuel-consumption units. The general Unit Converter complements these tools rather than duplicating their full functionality.
A unit conversion should preserve the quantity while changing how it is expressed. Reliable conversions depend on using the correct unit definition, distinguishing similar units such as U.S. and Imperial gallons, using proper formulas for non-linear conversions such as temperature, and keeping adequate precision until the final answer. CalculateThisWay makes the conversion fast while also showing enough of the math for you to understand where the result came from.
The values below are computed live in JavaScript using the same conversion engine as the calculator above, so they will always match what the calculator itself returns for these inputs.
Convert 5 feet to inches. What formula would you use?
5 feet × 12 = 60 inches, since 1 foot equals exactly 12 inches.
I already know a measurement and just need it in a different unit.
I want to convert a height between feet/inches and centimeters in one combined field.
I want to calculate an area from room length and width measurements.
I want to solve for speed, distance, or time, not just convert a speed unit.
I want MPG, km/L, or fuel-consumption calculations.
A unit converter changes a measurement expressed in one unit into the equivalent measurement in a different unit, while the underlying physical quantity stays exactly the same.
Multiply the number of inches by 2.54. For example, 10 inches times 2.54 equals 25.4 centimeters.
There are exactly 2.54 centimeters in one inch.
There are exactly 30.48 centimeters in one foot, since one foot contains 12 inches and each inch equals 2.54 centimeters.
Multiply the number of feet by 0.3048. One international foot equals exactly 0.3048 meters.
Divide centimeters by 2.54 to get total inches, then divide that number of inches by 12 to get feet.
Multiply the number of miles by 1.609344. One international mile equals exactly 1.609344 kilometers.
There are exactly 1.609344 kilometers in one international mile.
Multiply the number of pounds by 0.45359237. One international pound equals exactly 0.45359237 kilograms.
One kilogram equals approximately 2.20462 pounds.
One ounce equals exactly 1/16 of a pound, which works out to approximately 28.349523125 grams.
Multiply the Celsius value by 9/5, then add 32. For example, 20 Celsius times 9/5 equals 36, plus 32 equals 68 Fahrenheit.
Subtract 32 from the Fahrenheit value, then multiply by 5/9. For example, 68 minus 32 equals 36, times 5/9 equals 20 Celsius.
Add 273.15 to the Celsius value. For example, 0 Celsius plus 273.15 equals 273.15 Kelvin.
No. Zero Kelvin represents absolute zero, the coldest physically possible temperature, so negative Kelvin values are not valid.
Divide liters by 3.785411784 to get US gallons, or divide by 4.54609 to get Imperial gallons, since the two gallon definitions are not the same.
No. A US gallon equals 3.785411784 liters, while an Imperial gallon equals 4.54609 liters, so an Imperial gallon is noticeably larger.
No. A US cup equals about 236.59 milliliters, while a metric cup is commonly defined as 250 milliliters, so recipes should state which cup they mean.
Multiply square feet by 0.09290304. This is the squared version of the length factor, not the plain 0.3048 foot-to-meter factor.
Area measures two dimensions at once, so when a length factor is applied to both dimensions, the conversion factor itself becomes squared rather than staying linear.
One acre equals exactly 43,560 square feet.
Multiply hectares by approximately 2.47105 to get acres, since one hectare equals 10,000 square meters and one acre equals 4,046.8564224 square meters.
Multiply miles per hour by 1.609344. For example, 60 mph times 1.609344 equals 96.56064 km/h.
Divide kilometers per hour by 1.609344. For example, 100 km/h divided by 1.609344 is about 62.137 mph.
A knot is one nautical mile per hour, commonly used in marine navigation, aviation, and weather reporting. It is not the same as one mph.
Small differences usually come from rounding settings, older conversion factors, mixing up US and Imperial units, or using the deprecated US survey foot instead of the international foot.
Many common conversion factors, such as inches to centimeters or pounds to kilograms, are defined exactly. The displayed result may still be rounded for readability.
For everyday use, two to four decimal places is usually enough. Scientific or technical work may call for more precision, which this calculator's Decimal Places option supports.
SI, the International System of Units, is the modern metric system maintained internationally by the Bureau International des Poids et Mesures, using base units such as the meter, kilogram, second, and kelvin.
The metric system is a decimal measurement system built around SI units and prefixes, so moving between related units, such as meters and kilometers, means multiplying or dividing by powers of ten.
Not technically. Mass measures the amount of matter in an object, while weight measures the force of gravity on that mass. Everyday conversions between pounds and kilograms treat both as units of mass.
The international foot is the modern, globally agreed definition equal to exactly 0.3048 meters, and it is the foot used for ordinary consumer length conversions.
The U.S. survey foot was a slightly different, older definition used mainly in land surveying. It was officially phased out in favor of the international foot for most practical purposes.