Why does my hard drive show less space than advertised?

The drive is labeled using decimal units, where 1 TB is 10¹² bytes, but your operating system may count in binary units, where 1 TiB is 2⁴⁰ bytes. The same number of bytes looks about 9% smaller in binary terms. Formatting and system files take a little more.

What is the difference between Mbps and MB/s?

Mbps means megabits per second, and MB/s means megabytes per second. There are 8 bits in a byte, so a 100 Mbps connection transfers at most about 12.5 MB/s before overhead. Internet plans are usually sold in Mbps.

Is a calorie on a food label the same as a calorie in physics?

No. A food Calorie (often written with a capital C or as kcal) is 1,000 small calories, about 4,184 joules. Physics and chemistry usually use the small calorie of about 4.184 joules.

How do I convert horsepower to watts?

One mechanical horsepower is about 745.7 watts, so multiply horsepower by 745.7, or by 0.7457 for kilowatts. Metric horsepower is slightly smaller, at about 735.5 watts, and is used in some European specifications.

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Unit Conversions calculators

These converters handle length, mass, volume and other everyday units, along with temperature, speed, angles, fuel efficiency, pressure, energy, power, data storage and number bases. They use exact defined conversion factors where they exist, so a result is as precise as your input.

10 tools · Updated October 21, 2026

Showing 10 tools

⇄Angle ConverterEveryday measurements90° in radiansπ/2 ≈ 1.5707963 rad

⇄Data Storage ConverterDigital units1 TB in GiB931.32257 GiB

⇄Energy ConverterPressure, energy and power1 kWh in BTU3,412.1416 BTU

⇄Fuel Efficiency ConverterEveryday measurements30 mpg (US) in L/100 km7.8405 L/100 km

0xNumber Base ConverterDigital units255 in binary and hexadecimal1111 1111, 0xFF

⇄Power Unit ConverterPressure, energy and power1 hp in kW0.74569987 kW

⇄Pressure Unit ConverterPressure, energy and power32 psi in kPa220.63223 kPa

⇄Speed ConverterEveryday measurements60 mph in km/h96.56064 km/h

°FTemperature ConverterEveryday measurements20 °C in Fahrenheit68 °F

⇄Unit ConverterEveryday measurements1 mi in km1.609344 km

Which one do I need?

I need to convert length, weight or volume between metric and US unitsUnit Converter I want Celsius, Fahrenheit and Kelvin at the same timeTemperature Converter I want to convert mph, km/h, m/s or knotsSpeed Converter I want to compare MPG with liters per 100 kmFuel Efficiency Converter I need psi, bar, kPa or atm conversionsPressure Unit Converter I want to convert joules, kWh, BTU or food caloriesEnergy Converter I want to know how many GB or GiB a file or drive really isData Storage Converter I need to convert a number between binary, decimal and hexadecimalNumber Base Converter

Metric, US customary and exact definitions

Since 1959, US customary units have been defined in terms of metric ones: an inch is exactly 2.54 cm and a pound is exactly 0.45359237 kg. That means conversions between them are exact, not approximations. The Unit Converter uses these defined values, which matters when small errors would compound across many items.

Watch for units that share a name but differ in size. A US gallon is about 3.785 liters while an imperial gallon is about 4.546; a US fluid ounce differs from an imperial one; and a short ton (2,000 lb) is lighter than a metric tonne (1,000 kg). Check which system a recipe, specification or label uses before converting.

Conversions that are not a simple factor

Most conversions multiply by a constant, but temperature also shifts the zero point: °F = °C × 9/5 + 32, while kelvin starts at absolute zero. That is why a temperature difference of 10 °C is 18 °F, but a temperature of 10 °C is 50 °F. The Temperature Converter shows Celsius, Fahrenheit, Kelvin and Rankine together to avoid this confusion.

Fuel efficiency is inverted between systems. Miles per gallon measures distance per fuel, while liters per 100 km measures fuel per distance, so the conversion is a division (about 235.2 ÷ US mpg). The Fuel Efficiency Converter also reveals that improving a car from 10 to 20 mpg saves more fuel than going from 30 to 50 mpg over the same distance.

Data sizes and number bases

Storage makers use decimal prefixes (1 GB = 1,000,000,000 bytes), while many operating systems report sizes in binary units (1 GiB = 1,073,741,824 bytes) and sometimes still label them GB. That is why a new 1 TB drive shows up as roughly 931 GB. The Data Storage Converter shows both, and also distinguishes bits from bytes, a factor of eight that matters for download speeds.

The Number Base Converter moves values between binary, octal, decimal and hexadecimal, the bases that appear in programming, networking and color codes.

Questions people ask

Yes, −40 degrees. At that point −40 °C equals −40 °F, which follows from solving C = C × 9/5 + 32. It is a handy check for any temperature formula.