Everyday math
Unit Converter: Convert Common Measurements In Seconds
Last updated: October 2026
Written by Jessica Hill
A unit converter changes a measurement from one unit to another by multiplying by a conversion factor. For example, inches × 2.54 = centimeters, and miles × 1.609344 = kilometers. Temperature is the exception: it uses a formula, °C = (°F − 32) × 5/9, because the scales start at different zero points.
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Most conversions need one factor and one multiplication. Below are the factors you will use most and the conversions that trip people up.
How Unit Conversion Works
Every conversion multiplies by a factor equal to 1, written as a fraction of matching amounts. Since 1 inch equals 2.54 cm, the fraction 2.54 cm / 1 in is equal to 1, so multiplying by it changes the units without changing the amount.
For conversions with more than one step, chain the fractions so the units cancel. Converting 60 miles per hour to meters per second:
60 mi/h × 1,609.344 m/mi × 1 h/3,600 s = 26.82 m/s
If "mi" and "h" cancel and "m/s" is left, the setup is right.
Common Conversion Factors
Many U.S. customary units are now defined exactly in metric terms. The inch is exactly 2.54 cm, the foot is exactly 0.3048 m, and the mile is exactly 1,609.344 m, as listed in NIST's official conversion factors.
| Category | From | To | Multiply by |
|---|---|---|---|
| Length | inches | centimeters | 2.54 (exact) |
| Length | feet | meters | 0.3048 (exact) |
| Length | miles | kilometers | 1.609344 (exact) |
| Length | meters | feet | 3.28084 |
| Weight | pounds | kilograms | 0.453592 |
| Weight | kilograms | pounds | 2.20462 |
| Weight | ounces | grams | 28.3495 |
| Volume | US gallons | liters | 3.78541 |
| Volume | US cups | milliliters | 236.588 |
| Volume | US fluid ounces | milliliters | 29.5735 |
| Area | square yards | square feet | 9 |
| Speed | mph | km/h | 1.609344 |
Divide to go the other way. For area conversions in detail, including acres and hectares, see the area calculator.
Temperature Conversions
Temperature uses formulas instead of a single factor, because Fahrenheit, Celsius and Kelvin start at different zero points.
| Convert | Formula | Example |
|---|---|---|
| °F to °C | (°F − 32) × 5/9 | 70 °F → 21.1 °C |
| °C to °F | °C × 9/5 + 32 | 37 °C → 98.6 °F |
| °C to K | °C + 273.15 | 25 °C → 298.15 K |
A useful check: −40 is the same in both scales. For a mental estimate, double the Celsius value and add 30.
US Customary, Imperial And Metric
The United States mostly uses customary units, while most of the world uses metric. The UK uses a mix, including imperial units that share names with U.S. units but are not the same size.
The biggest trap is volume. A U.S. gallon is about 3.785 liters, while a UK imperial gallon is 4.546 liters, about 20 percent larger. U.S. and UK pints and fluid ounces also differ. Check which system a recipe or spec sheet uses.
Length got simpler recently. The U.S. survey foot, once used in land surveying, was retired after December 31, 2022. Since then, only the international foot of exactly 0.3048 m applies.
Conversions That Trip People Up
A few conversions break the "multiply by one factor" habit.
- Area and volume. Square and cube the factor. One yard is 3 feet, but one square yard is 9 square feet and one cubic yard is 27 cubic feet.
- Data storage. Drive makers use decimal units (1 TB = 1,000,000,000,000 bytes), while many computers report binary units. That is why a 1 TB drive shows about 931 GiB.
- Bits and bytes. Internet speeds are in megabits per second (Mbps). Divide by 8 for megabytes per second.
- Fuel economy. Miles per gallon and liters per 100 km are inverses, so you divide instead of multiply: L/100 km = 235.21 ÷ mpg. So 30 mpg is about 7.84 L/100 km.
How To Check A Conversion
Converting to a smaller unit, like meters to centimeters, gives a bigger number. Converting to a larger unit gives a smaller number. If your answer moves the wrong way, you multiplied when you should have divided.
For long chains of factors, the scientific calculator keeps every digit.
Summary
- Most conversions multiply by one factor, like 2.54 for inches to centimeters.
- Chain fractions and cancel units for multi-step conversions.
- Temperature uses formulas, not factors.
- Square or cube the factor for area or volume, and watch U.S. vs UK units.
- Sanity-check the direction: smaller units mean bigger numbers.
Next step: enter your value in the unit converter at the top of this page, or explore more tools on the Calc Solver homepage.
Frequently Asked Questions
How many centimeters are in an inch?
There are exactly 2.54 centimeters in one inch. This value has been the official definition since 1959. To convert inches to centimeters, multiply by 2.54. To go from centimeters to inches, divide by 2.54, or multiply by about 0.3937. For example, a 12-inch ruler is 30.48 cm long.
How do I convert feet and inches to centimeters?
Turn the whole height into inches first, then multiply by 2.54. For 5 ft 10 in, that is 5 × 12 + 10 = 70 inches, and 70 × 2.54 = 177.8 cm. Converting the feet and inches separately and adding also works: 152.4 cm + 25.4 cm = 177.8 cm.
Is a kilogram the same as 2.2 pounds?
Close, but not exactly. One kilogram is about 2.20462 pounds. Using 2.2 is fine for everyday estimates, but the small difference adds up. For 100 kg, using 2.2 gives 220 pounds, while the precise answer is about 220.46 pounds.
What is the difference between mass and weight?
Mass is the amount of matter in an object, measured in kilograms or pounds-mass. Weight is the force gravity puts on that mass, measured in newtons or pounds-force. On Earth, the two are used interchangeably in daily life. On the Moon, your mass stays the same, but your weight drops to about one-sixth.
Why does the U.S. still use customary units?
The U.S. kept the inch, pound and gallon from its British roots, and switching everything over has never been required by law for everyday use. Science, medicine and much of manufacturing in the U.S. already use metric. That is why unit conversion comes up so often in American schools and jobs.
Try it with your own numbers
Use a free CalcSolver tool to check the examples in this guide.