Unit Converter
5 kilometers equals 3.106856 miles, and 150 pounds equals 68.038855 kilograms. This unit converter handles the three measurement groups people look up most often: length, weight, and temperature. Pick a conversion type, enter a value, choose the unit you already have, and choose the unit you need, and the tool returns the converted figure instantly. Length covers millimeters through miles, weight covers milligrams through pounds and ounces, and temperature covers Celsius, Fahrenheit, and Kelvin using the correct scale equations instead of a simple multiplier. It is built for the everyday moments where a recipe, a shipping label, a workout log, a travel itinerary, or a homework problem gives you a number in one unit and you need it in another, without pulling out a reference chart or doing the base-unit math by hand.
Quick answer
Select a conversion type first: length, weight, or temperature. Each group has its own set of supported units.
What this tells you
- •Select a conversion type first: length, weight, or temperature. Each group has its own set of supported units.
- •Length and weight conversions route through a shared base unit (meters for length, kilograms for weight), which keeps every unit pair consistent.
- •Temperature conversions use the actual Celsius, Fahrenheit, and Kelvin formulas because those scales are offset, not simply scaled, so a single multiply-and-divide step would not work.
- •Results are rounded to 6 decimal places for readability, while the underlying math uses full-precision standard conversion factors.
- •The tool accepts common metric and imperial units side by side, so you can move between systems in one step instead of converting twice.
How to Use
- 1Choose a conversion type: length, weight, or temperature.
- 2Enter the value you want to convert. Decimals are fine, so values like 5.5 or 0.125 work.
- 3Enter the source unit you already have, such as km, lb, or C.
- 4Enter the target unit you want to see, such as mi, kg, or F.
- 5Calculate to see the converted value along with the unit labels and the conversion used.
How It Works
Formula
Length or weight: converted value = input × (source-to-base factor) ÷ (target-to-base factor)
Temperature: convert to Celsius first, then apply the C-to-target formulaLength conversions run through meters as the base unit, and weight conversions run through kilograms. The tool multiplies your input by the source unit's factor to get a base value, then divides by the target unit's factor to get the final answer. For example, 5 km becomes 5 × 1000 = 5000 meters, and dividing by the mile factor of 1609.344 gives 3.106856 mi. Temperature cannot use this same multiply-and-divide shortcut because Celsius, Fahrenheit, and Kelvin have different zero points, not just different step sizes. The tool always converts the input to Celsius first using C = value, C = (F − 32) × 5⁄9, or C = K − 273.15, then converts that Celsius figure to the target scale using F = C × 9⁄5 + 32 or K = C + 273.15.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Length conversion example
Five kilometers equal 5000 meters. Dividing 5000 by the mile factor of 1609.344 gives 3.106856 mi. This kind of conversion comes up when a race distance, road sign, or travel itinerary is listed in kilometers but you think in miles, or the other way around.
Weight conversion example
One pound equals 0.45359237 kilograms, so 150 pounds equal 150 × 0.45359237 = 68.038855 kg. This is a common check for body weight readings, luggage limits, or shipping weights when a form or scale expects kilograms instead of pounds.
Temperature conversion example
Subtract 32 from 98.6 to get 66.6, then multiply by 5⁄9 to get 37. A normal human body temperature of 98.6°F converts to exactly 37°C, which is why that pair of numbers shows up so often in health and cooking contexts alike.
Length conversion example: miles to kilometers
One mile is defined as exactly 1609.344 meters, which is 1.609344 kilometers. This fixed factor is why a 26.2-mile marathon is commonly listed as 42.195 kilometers on international race materials.
Weight conversion example: grams to ounces
Since one ounce equals 28.349523125 grams, 500 grams divided by that factor gives 17.636981 oz. Recipes and food packaging often list weight in grams internationally and ounces in the US, so this conversion comes up frequently in the kitchen.
Checked-bag limit in kilograms, bathroom scale in pounds
Priya's airline sets a 23 kg limit for checked bags, but her scale at home reads in pounds. Dividing 23 by the exact pound factor of 0.45359237 gives 50.70632 lb. Multiplying by the rounded 2.2 most people remember would give 50.6 lb, about 0.1 lb low. That gap is small here, but it shows why the tool keeps the full factor instead of a shortcut.
Exact conversion factors defined by agreement
These values are exact by definition, not measured, so a conversion built on them carries no rounding error until the final display.
| Unit | Equals | Exact or derived | Defined by |
|---|---|---|---|
| 1 inch | 25.4 mm | Exact, defining value | 1959 international yard and pound agreement |
| 1 foot | 0.3048 m | Exact, derived from 12 inches | 1959 agreement |
| 1 yard | 0.9144 m | Exact, derived from 3 feet | 1959 agreement |
| 1 mile | 1,609.344 m | Exact, derived from 5,280 feet | 1959 agreement |
| 1 pound (avoirdupois) | 0.45359237 kg | Exact, defining value | 1959 agreement |
| 1 ounce (avoirdupois) | 28.349523125 g | Exact, derived from 1/16 pound | 1959 agreement |
| 1 US gallon | 231 cubic inches = 3.785411784 L | Exact, derived from the inch | NIST Handbook 44, Appendix C |
| 1 US fluid ounce | 29.5735295625 mL | Exact, derived from 1/128 US gallon | NIST Handbook 44, Appendix C |
| 1 acre | 4,046.8564224 square meters | Exact, derived from 4,840 square yards | 1959 agreement yard |
| 1 kilowatt-hour | 3.6 MJ | Exact, derived from 1 kW x 3,600 s | NIST SP 811, Appendix B |
| Fahrenheit from Celsius | F = C x 9/5 + 32 | Exact scale relationship | NIST SP 811, Appendix B |
Sources: NIST Special Publication 811 (2008), Appendix B, and NIST Handbook 44, Appendix C. The inch and pound values were fixed by the 1959 agreement among the national standards laboratories of the United States, the United Kingdom, Canada, Australia, New Zealand, and South Africa. Only the length, weight, and temperature rows are units this converter accepts. The volume, area, and energy rows are here for reference.
Why exact conversion factors matter
A rounded factor looks harmless until it gets reused. Converting a 10 km run with 0.62 miles per kilometer gives 6.2 miles, while the exact factor gives 6.213712 miles, a gap of about 72 feet. Multiply 23 kg by the rounded 2.2 and you get 50.6 lb instead of 50.70632 lb. Chain two or three rounded steps, such as kilograms to pounds to ounces and back, and the errors stack instead of canceling. This converter always multiplies by the full defining factor and rounds once, at the display.
The word gallon does not mean the same thing on both sides of the Atlantic. A US gallon is 231 cubic inches, or 3.785411784 liters, and holds 128 US fluid ounces of 29.5735295625 mL each. The imperial gallon used in the United Kingdom is 4.54609 liters and holds 160 imperial fluid ounces of 28.4130625 mL each, so an imperial pint is 568.26125 mL against a US pint of 473.176473 mL. NIST Special Publication 811, Appendix B, lists both gallons. A recipe or fuel-economy figure from a UK source needs the imperial values, not the US ones.
Length had a similar split inside the United States until recently. The 1959 agreement set the international foot at exactly 0.3048 m, but U.S. land surveying kept the older U.S. survey foot of 1200/3937 m, about 0.3048006 m. The two differ by about 3.2 mm per mile, enough to matter across state plane coordinates. NIST and the National Geodetic Survey retired the survey foot effective January 1, 2023, so the international foot is now the only foot for new work. Every length conversion on this page has always used the international foot.
The converter itself has fixed limits. It applies constant factors from NIST SP 811, Appendix B, to length and weight units only, and it has no volume, area, or energy units, so US and imperial gallons alike are outside its range even though the table above lists the US values for reference. Its ounce factor is the exact 28.349523125 g, one sixteenth of the defined pound. Temperature is not a ratio conversion at all: the SI Brochure (BIPM, 9th edition) defines Celsius as an offset from kelvin, t = T minus 273.15, and Fahrenheit adds a second offset of 32, so the tool converts through Celsius with those affine formulas rather than a single multiplier. Doubling a temperature in one scale never doubles it in another.
Common mistakes
- Applying a length factor to a weight value or vice versa. Each conversion group has its own set of supported units, and mixing them returns no result rather than a wrong one.
- Assuming temperature scales as a straight multiplier. Doubling a Celsius value and converting to Fahrenheit does not double the Fahrenheit reading, because the scales have different zero points.
- Mistyping a unit abbreviation, such as entering "kgs" instead of "kg" or "F" written as "fahrenheit." The tool matches supported abbreviations exactly, so an unrecognized label is rejected.
- Confusing mass and weight in casual language. This tool converts mass units like kilograms and pounds, which is what people mean in daily use even though "weight" and "mass" are technically different in physics.
- Rounding an intermediate result before converting again. Chaining a rounded output into a second manual conversion compounds small errors, so convert directly from the original value instead.
Embed this calculator on your site
Paste this code where you want the calculator to appear. It is responsive, mobile-friendly, resizes automatically, and is free to use as long as the credit line stays in place.
<script src="https://calctide.com/embed.js" data-tool="unit-converter" async></script>
<p style="font-size:12px;margin:4px 0 0">Unit Converter by <a href="https://calctide.com/converters/unit-converter/">CalcTide</a></p>Preview the embed at /embed/unit-converter/.