Scientific unit converter
Energy, force, pressure, power, speed, area, and time — built for physics homework, chemistry tables, and engineering back-of-the-envelope work. Scientific notation input is supported throughout (try 1.5e-19).
Scientific notation OK — try 1.5e-19
The joule is named after James Prescott Joule, an English brewer who established that heat is a form of energy. He apparently took thermometers on his honeymoon to measure the temperature of waterfalls — to test his theory that falling water heats up.
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Frequently asked questions
How do I convert calories to joules?
Multiply calories by 4.184 to get joules — that is the thermochemical calorie used in chemistry and physics. So 100 cal is 418.4 J, and 1 kcal (also written Cal or food calorie) is exactly 4184 J. The international-table calorie is slightly different at 4.1868 J per cal but is rarely used in modern textbooks.
What is 1 electronvolt in joules?
One electronvolt (eV) is exactly 1.602176634 × 10⁻¹⁹ joules — that value was fixed by the 2019 redefinition of the SI base units. The electronvolt is the kinetic energy gained by an electron accelerated through a potential difference of one volt. Common related values: 1 keV is 1.602 × 10⁻¹⁶ J, and the rest energy of an electron is about 0.511 MeV.
How many pascals is 1 atmosphere?
One standard atmosphere (atm) is exactly 101325 Pa, or 101.325 kPa, or 1.01325 bar. Other useful pressure equivalents: 1 atm equals 760 mmHg (also called 760 Torr), and approximately 14.696 psi. The atmosphere is a non-SI unit but is still widely used in chemistry for tabulating gas data.
How do I convert mph to m/s?
Multiply miles per hour by 0.44704 to get metres per second. So 60 mph is 26.82 m/s, 70 mph is 31.29 m/s, and 100 mph is 44.70 m/s. To go the other way, multiply m/s by 2.23694. A handy mental check: walking pace is about 1.4 m/s, sprinting is roughly 10 m/s, and motorway speed limits sit around 30 m/s.
How many watts is 1 horsepower?
One mechanical horsepower (used in the US and UK) is approximately 745.7 W. The metric horsepower (PS or CV, used on European car spec sheets) is slightly smaller at 735.5 W. The difference comes from how each unit was historically defined: mechanical horsepower is exactly 550 ft·lbf per second, metric horsepower is 75 kgf·m per second.
What is the difference between a calorie and a Calorie?
In physics and chemistry, a small calorie (cal) is the energy needed to raise one gram of water by one degree Celsius — about 4.184 J. In nutrition, the "Calorie" with a capital C is actually a kilocalorie (kcal) — one thousand small calories, or about 4184 J. So when a food label says 200 Calories, it really means 200 kcal, or 837 kJ.
How do I convert square metres to square feet?
Multiply square metres by 10.7639 to get square feet. So 50 m² is 538 ft², 100 m² is 1076 ft², and a hectare (10000 m²) is about 107639 ft² or 2.47 acres. Note that area conversions are the square of the linear conversion: 1 ft is 0.3048 m, so 1 ft² is 0.3048² = 0.09290304 m².
Can I enter scientific notation directly?
Yes — type values like 1.5e-19 or 6.022e23 into the value field and they are parsed correctly. The result will switch to scientific notation automatically when fixed-point would be unreadable (more than six leading zeros, or values above one billion). You can also force scientific notation with the toggle below the input.