Convert between bar and PSI and find recommended pressures for your tyres
Maintaining correct tyre pressure is one of the simplest yet most important aspects of vehicle safety and economy in the UK. According to TyreSafe, the UK tyre safety charity, around 57% of tyres on UK roads are under-inflated, contributing to increased fuel consumption, accelerated tyre wear, and compromised road safety. In the UK, tyre pressure is commonly expressed in bar (the metric standard), though many vehicles -- particularly those with American or Japanese origins -- also display pressures in PSI (pounds per square inch). The conversion between the two is straightforward: 1 bar equals 14.5038 PSI. Most UK garages and petrol station air machines accept both units, but knowing the conversion is essential when switching between sources of information. Your vehicle manufacturer specifies different pressures for front and rear tyres, and higher pressures when carrying heavy loads or towing. These recommendations are calibrated for your specific vehicle's weight distribution, suspension geometry, and handling characteristics. Running at the correct pressure ensures even tyre wear, optimal fuel efficiency, safe braking distances, and predictable handling. This calculator converts between bar and PSI and shows recommended pressures for both normal and loaded conditions.
To use the tyre pressure calculator: 1. Enter your tyre pressure value. You can find the recommended pressure on a sticker inside the driver's door frame, inside the fuel filler cap, or in your vehicle handbook. If you cannot find the sticker, the handbook or manufacturer's website will list the correct pressures for your specific model and tyre size. 2. Select the unit of the value you entered. Choose bar if your vehicle sticker shows values like 2.2 or 2.5, or PSI if it shows values like 32 or 36. The calculator will convert to the other unit automatically. 3. Select the load condition. Choose normal load for everyday driving with 1-2 passengers. Select fully loaded when carrying a full complement of passengers and luggage, or when towing a trailer. The loaded condition adds approximately 0.3 bar (4 PSI) to account for the increased weight. 4. Review the results. The calculator shows the converted pressure in both units, the recommended front and rear pressures (rear tyres typically run 0.1 bar / 1.5 PSI higher than front), and the loaded pressures for when you are carrying extra weight. 5. Always check tyre pressure when the tyres are cold -- ideally before driving or after driving less than two miles. Hot tyres give a higher reading that can be misleading. If you must check at a petrol station, add 4-5 PSI to compensate for the heat generated during driving, then recheck when cold at home.
The tyre pressure calculations are based on simple unit conversion and industry-standard adjustments: **Bar to PSI Conversion:** PSI = pressure in bar x 14.5038 For example, 2.2 bar = 2.2 x 14.5038 = 31.9 PSI. **PSI to Bar Conversion:** Bar = pressure in PSI / 14.5038 For example, 32 PSI = 32 / 14.5038 = 2.21 bar. **Front and Rear Split:** Rear pressure = front pressure + 0.1 bar (approximately 1.5 PSI) Most vehicles specify slightly higher rear tyre pressure to account for weight distribution, particularly when carrying rear passengers and boot luggage. The 0.1 bar offset is a common default, though your specific vehicle may vary. **Loaded Condition Adjustment:** Loaded pressure = normal pressure + 0.3 bar (approximately 4 PSI) When carrying a full load of passengers and luggage, increasing pressure by 0.3 bar helps the tyres support the additional weight without excessive sidewall flex. This reduces the risk of tyre overheating, maintains handling stability, and prevents premature inner-edge wear. **Why Correct Pressure Matters:** Under-inflation by just 0.3 bar (4 PSI) increases fuel consumption by approximately 1-2%, reduces tyre life by up to 25%, and lengthens braking distances. Over-inflation reduces the contact patch, leading to reduced grip, a harsher ride, and accelerated centre-tread wear. UK MOT tests do not specifically check tyre pressure, making regular self-checks essential. The conversion factor of 14.5038 PSI per bar is exact to four decimal places and is the internationally accepted standard used by tyre manufacturers and vehicle makers worldwide.