How to Use This Unit Converter
This conversion tool handles six primary physical domains with standardized conversion factors defined by the International System of Units (SI) and the National Institute of Standards and Technology (NIST):
- Select Category: Pick from Length, Weight, Temperature, Volume, Area, or Speed using the top dropdown.
- Input Value: Enter the quantity you wish to convert in the numeric field.
- Choose Units: Choose your source unit ("From") and target unit ("To"). Output and exact mathematical conversion factors update immediately.
How Conversions Work Across Different Scales
Most physical measurement units relate to one another linearly through a multiplicative conversion constant via a base SI unit:
Temperature Celsius to Fahrenheit: °F = (°C × 9/5) + 32
Temperature Fahrenheit to Celsius: °C = (°F − 32) × 5/9
Celsius to Kelvin: K = °C + 273.15
Because temperature scales measure thermodynamic thermal energy with distinct zero points (Kelvin has absolute zero at 0 K, whereas Celsius sets water's freezing point at 0 °C and Fahrenheit sets it at 32 °F), temperature requires both scaling and offset shifts.
Step-by-Step Worked Example
Worked Example: Converting Kilometers per Hour to Miles per Hour
A car is traveling on a European highway at 120 km/h. What is the equivalent speed in miles per hour (mph)?
- Conversion factor: 1 kilometer = 0.621371 miles.
- Multiply speed: 120 km/h × 0.621371 = 74.56 mph.
- Conclusion: 120 km/h is approximately 74.6 mph, typical highway cruising speed.
Frequently Asked Questions
What is the difference between US fluid ounces and ounces of weight?
A fluid ounce (fl oz) is a measure of liquid volume equal to 1/128th of a US gallon (approximately 29.57 mL). An avoirdupois ounce (oz) is a measure of mass/weight equal to 1/16th of a pound (approximately 28.35 grams). They are distinct units measuring different physical properties.
Why does -40° have the same value in Celsius and Fahrenheit?
Solving the equation $C = (C imes 9/5) + 32$ gives $C - 1.8C = 32$, which simplifies to $-0.8C = 32$, yielding $C = -40$. Thus, $-40 ext{ }^\circ ext{C} = -40 ext{ }^\circ ext{F}$.
Are conversion factors exact?
Yes. International agreements (such as the 1959 International Yard and Pound Agreement) formally define imperial units in terms of exact metric values. For instance, 1 inch is defined as exactly 25.4 millimeters, and 1 pound is defined as exactly 0.45359237 kilograms.
How many acres are in a square mile?
One square mile contains exactly 640 acres. A square kilometer contains approximately 247.105 acres or 100 hectares.