Precision unit conversion
These three units are grouped together because they turn up in the same practical situations — checking tyre pressure, comparing appliance energy use, or working out horsepower versus kilowatts for a vehicle or motor.
Tyre pressures, weather reports and gas cylinders all use different pressure units. 1 bar equals 100,000 pascals and is roughly atmospheric pressure at sea level (1 atmosphere = 1.01325 bar).
| Convert | Result |
|---|---|
| 1 bar | 14.5038 psi (100 kPa) |
| 1 psi | 0.0689476 bar (6,894.76 Pa) |
| 1 atmosphere | 1.01325 bar / 14.6959 psi |
| 32 psi (typical tyre) | 2.207 bar |
Food energy is usually given in kilocalories (what nutrition labels call "Calories" with a capital C), while electricity bills use kilowatt-hours, and scientific work uses joules. All three measure the same underlying quantity — energy — just scaled differently.
| Convert | Result |
|---|---|
| 1 kilocalorie (kcal) | 4,184 J (4.184 kJ) |
| 1 kilowatt-hour (kWh) | 3,600,000 J (3.6 MJ) |
| 1 BTU | 1,055.06 J |
| 2,000 kcal (daily intake) | 8,368 kJ |
Power is energy per unit time. Vehicle and motor power is often quoted in horsepower in the UK and US, while electrical appliances and modern engine specs increasingly use kilowatts.
| Convert | Result |
|---|---|
| 1 horsepower (hp) | 745.7 W (0.7457 kW) |
| 1 kilowatt (kW) | 1.34102 hp |
| 100 hp | 74.57 kW |
| 150 kW | 201.2 hp |
Open the live converter for the specific category you need — pressure, energy or power each have their own dedicated tab with all the relevant units.
Multiply bar by 14.5038. So 2 bar is about 29.01 psi — a typical car tyre pressure is often around 2.1–2.4 bar (30–35 psi).
One kilocalorie (the "Calorie" shown on food labels) is 4,184 joules.
Multiply horsepower by 0.7457. So a 200 hp engine is about 149.1 kW.
A food label's "Calorie" (capital C) is actually a kilocalorie — 1,000 small calories — which is a labelling convention that causes confusion, since the scientific "calorie" (lowercase) is a much smaller unit.