Physics Unit Converter — Joules, Newtons, Watts, Pascals and More
Physics problems regularly require converting between SI units and engineering units: joules to kilowatt-hours, newtons to pound-force, watts to horsepower, pascals to PSI. The free physics unit converter on PublicSoftTools covers five categories with instant conversion across all units.
Key Unit Conversions Reference
| From | To (SI base) | Category |
|---|---|---|
| 1 kWh | 3,600,000 J | Energy |
| 1 kcal (food calorie) | 4,184 J | Energy |
| 1 eV | 1.602 × 10⁻¹⁹ J | Energy |
| 1 BTU | 1,055.06 J | Energy |
| 1 hp (mechanical) | 745.7 W | Power |
| 1 lbf (pound-force) | 4.448 N | Force |
| 1 kgf | 9.807 N | Force |
| 1 atm | 101,325 Pa | Pressure |
| 1 bar | 100,000 Pa | Pressure |
| 1 PSI | 6,894.76 Pa | Pressure |
| 100 km/h | 27.78 m/s | Velocity |
| 60 mph | 26.82 m/s | Velocity |
How to Use the Converter
- Open the physics unit converter.
- Select the category at the top: Energy, Force, Power, Pressure, or Velocity.
- Choose the source unit in the left dropdown and enter the value.
- Choose the target unit in the right dropdown.
- The converted value appears instantly in the result field.
Energy Units in Depth
Energy appears in many units depending on the field:
- Joule (J) — the SI base unit. One joule is the energy to lift 102 g by 1 m against gravity.
- kWh — used by electricity utilities. One kWh = 3,600,000 J. Your electricity bill is in kWh.
- kcal — used in nutrition. A "200-calorie" food contains 200 kcal = 836,800 J.
- eV — used in atomic and nuclear physics. 1 eV = 1.602 × 10⁻¹⁹ J — the energy gained by an electron crossing 1 Volt of potential.
- BTU — used in US HVAC. Air conditioner capacity is rated in BTU/hr.
Pressure Units in Depth
Pressure is force per unit area. Different industries use different units:
- Pascal (Pa) — SI base unit. Very small: 1 Pa ≈ the pressure of a US banknote lying on a table.
- kPa / MPa — for larger pressures. Tire pressure ~230 kPa. Hydraulic systems ~10–30 MPa.
- bar — used in meteorology and scuba diving. 1 bar ≈ 1 atm ≈ 14.5 PSI.
- PSI — used in US industry and automotive. Car tire pressure is typically 30–35 PSI.
- mmHg / Torr — used in medicine. Normal blood pressure is ~120/80 mmHg.
Common Questions
Why use horsepower instead of watts for engines?
Horsepower (hp) became standard in the 19th century when James Watt needed to compare steam engine output to horse power. It persists by convention in the automotive industry. 1 hp = 745.7 W, so a 200 hp engine produces 149.1 kW of mechanical power.
What is the difference between weight (force) and mass?
Mass is measured in kilograms (kg) and is the same everywhere. Force (weight) is measured in Newtons — on Earth, a 1 kg mass weighs F = m × g = 1 × 9.81 = 9.81 N. Kilogram-force (kgf) is a non-SI unit equal to 9.807 N — the force exerted by 1 kg under standard gravity.
Convert Physics Units Now
Convert between energy, force, power, pressure, and velocity units instantly.
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