Scientific Unit Converter

How conversion through a base unit works

This converter handles five families of scientific units — energy, pressure, force, power, and frequency — and the trick that makes it accurate is the same in every category: each unit is defined relative to one base unit, and conversion always goes through that base. For energy the base is the joule (J); for pressure the pascal (Pa); for force the newton (N); for power the watt (W); for frequency the hertz (Hz). To convert from any unit to any other, the tool multiplies your value by the source unit's factor to reach the base, then divides by the target unit's factor. Because every conversion routes through SI base units with exact published factors, you avoid the rounding drift that creeps in when you chain unit-to-unit shortcuts. It all runs locally in your browser.

A worked example

Suppose you have 2 kWh and want it in BTU. One kilowatt-hour equals exactly 3,600,000 joules, so 2 kWh = 7,200,000 J. One BTU is 1,055.056 J, so dividing gives 7,200,000 ÷ 1,055.056 ≈ 6,824 BTU. The converter does both steps for you and, helpfully, shows the result in every unit of the category at once — so the same 2 kWh also appears as 7.2 × 10⁶ J, about 1,720 kcal, and so on. You enter one value and read off the whole row.

What each category covers

Two of these include conversions people regularly get wrong. The calorie in the energy list is the small thermochemical calorie (4.184 J); the "Calorie" on food labels is actually a kilocalorie, which is why kcal is listed separately at 4,184 J. And in the frequency list, rpm and rad/s are angular rates folded into the same group: 1 rpm = 1/60 Hz ≈ 0.01667 Hz, and 1 rad/s = 1/(2π) Hz ≈ 0.15915 Hz, because one full revolution is 2π radians.

The precision details that matter

The factors built into the tool are the exact defined values used in science and engineering: standard atmosphere is exactly 101,325 Pa, standard gravity makes 1 kgf exactly 9.80665 N, and the electronvolt uses the post-2019 SI definition of 1.602176634 × 10⁻¹⁹ J. Results are displayed to about eight significant figures for normal-magnitude numbers and switch to scientific notation for very large or very small ones — so converting energies down to electronvolts shows something like 6.241509 × 10¹⁸ rather than a meaningless string of zeros. Click Formula Reference to expand the exact relationships used for the current category.

Practical use cases

• Engineering datasheets. Convert a pump rated in psi to bar, or a motor rated in hp to kW, when comparing parts spec'd in different systems.
• Physics homework. Move between eV and joules for particle energies, or between erg and joule when a textbook uses CGS units.
• Weather and altitude. Translate barometric pressure between mmHg, hPa (kPa × 10), and inHg-adjacent atm values.
• Lab work. Reconcile force readings between kgf, N, and lbf on equipment from different manufacturers.

Common mistakes

• Treating kgf and kg as the same. A kilogram is mass; a kilogram-force is the weight that mass has under standard gravity. The converter handles kgf as force (9.80665 N) — never feed it a mass expecting a force.
• Mixing up calorie types. If your number came from a nutrition label, choose kcal, not cal. The factor of 1,000 between them is the single most common energy-conversion error.
• Forgetting horsepower has variants. This tool uses mechanical horsepower (745.7 W). Metric horsepower (PS) differs slightly at about 735.5 W; if your source quotes PS, the result will be off by roughly 1.4%.
• Confusing bar with atm. They are close but not equal — 1 bar = 100,000 Pa while 1 atm = 101,325 Pa, a 1.3% difference that matters in precise calculations.
• Reading rad/s as Hz directly. Angular frequency and ordinary frequency differ by a factor of 2π. The tool converts correctly, but do not equate the two numbers by eye.