Pressure, Energy and Power Converter
Convert pressure, energy and power units in one place. Each tab has its own From and To lists, the exact factor used, and a table of reference values.
Exact factors: 1 atm = 101,325 Pa, 1 bar = 100,000 Pa, 1 psi = 6894.757293 Pa. mmHg uses the conventional value 133.322387415 Pa.
Formula and calculation
Worked example
Tire pressure is quoted in both units. Converting 1 bar gives 14.5038 psi: the factor line reads 1 bar = 14.503774 psi, and a gauge showing 2.5 bar is 36.26 psi.
The same pressure, three different numbers
Weather reports use hectopascals or millibars, garages use bar or psi, and blood pressure is read in millimeters of mercury — all describing the same physical push. A tire at 2.4 bar is 240 kPa or 34.81 psi. A sea-level day at 1,013 hPa is 101.3 kPa or 14.69 psi. Blood pressure of 120/80 mmHg is 16.0 over 10.7 kPa. Because 1 bar is only 1.3% away from 1 atm, bar and atm can be swapped for rough work, but tire and gas line pressures are usually specified in one unit for a reason, so convert rather than guess.
Calories and BTU come in more than one version
Food labels use the kilocalorie: 1,000 thermochemical calories of exactly 4.184 J each, which is why a 2,000 kcal day is 8.368 MJ. The capital-C Calorie on US packaging is that same kilocalorie, not a small one. BTU is split the same way. This converter uses the International Table BTU of 1,055.05585262 J, the value in ISO 31-4 and most US engineering tables; the older thermochemical BTU is about 1,054.350 J, roughly 0.07% smaller. That gap is invisible in a furnace quote but visible in fuel data that names its convention, so check which one a table means before trusting the last digit.
What the results mean
- 1 bar =
- Your value in the target unit for the group selected on the tabs, converted with exact factors such as 1 atm = 101,325 Pa, 1 cal = 4.184 J and 1 hp = 745.699872 W.
- Conversion factor
- The one-way factor for this pair, so you can repeat the arithmetic by hand: value x factor = result.
- Reverse
- The same factor in the opposite direction, for converting a result back later.
Frequently asked questions
How many psi is 1 bar?
14.503774 psi, because a bar is exactly 100,000 Pa and a psi is 6,894.757293 Pa. For tire pressure, rounding to 14.5 psi is fine — a typical gauge is only accurate to a few percent anyway.
Is 1 atm exactly 101,325 Pa?
Yes, that is the definition of the standard atmosphere. It equals 101.325 kPa, 1.01325 bar, 14.695949 psi and 760 torr. Weather reports show it as 1,013.25 hPa.
Is mmHg the same as torr?
Almost. The conventional millimeter of mercury used here is exactly 133.322387415 Pa, while a torr is 1/760 of an atmosphere, 133.322368421 Pa — about one part in seven million apart. That is why 1 atm is 760 torr but only 759.99989 mmHg on this converter.
How many calories are in a kilowatt-hour?
One kWh is 3,600,000 J, which is 860.42 kcal or 3,412.14 BTU. That is also why an electric heater and a gas furnace are priced differently: the same energy costs whatever your kWh rate and your therm rate work out to.
How many watts is one horsepower?
745.699872 W for mechanical horsepower, the 550 ft·lbf/s unit used for car engines and motors. Metric horsepower (PS) is 735.49875 W and electric horsepower is exactly 746 W, so which label applies matters at the third digit.