How to convert Bar to PSI: a tyre pressure guide

Having the right tyre pressures is vitally important for maintaining the long-term health of your car or bike tyres. In this guide, we run through the basics and show how you can convert Bar to PSI.

Why does PSI and tyre pressure matter?

Monitoring your tyre pressure an important car maintenance job that’s often overlooked by drivers.

Having the correct tyre pressure means your tyres – that support the whole weight of your car and are the only contact point between your car and the road – operate correctly.

The right tyre pressure enhances your car’s grip levels, handling and ride comfort, while ensuring your braking performance and high-speed stability is as it should be.

Fuel economy is also dramatically affected when your tyres are running pressure below where they should be, because it takes more power from the engine to maintain the car’s speed.

Tyre tread wear is also affected by pressures that are too low or too high, meaning your tyres won’t last as long before they need replacing.

What PSI should my tyres be?

Tyre pressures vary depending on various factors, including the size and weight of the car and the size of the wheels. 

Most car tyre pressures vary anywhere between 30 to 40 PSI, often with different pressures for the front and rear tyres.

You'll need to find out your exact pressures for your car by checking the owner's manual, or by looking for a sticker in the driver's door frame.

This sticker will outline the pressures of your car for the exact size of wheel you have. They'll also show different pressures depending on how heavily loaded your car is, i.e. if you have a car full of passengers. 

Can you fail an MOT for low tyre pressures?

Technically, yes. Although the MOT test doesn't involve measuring tyre pressures, the examiners will visually inspect the tyre to ensure it's roadworthy and safe.

This includes checking it is correctly inflated and the tyre tread depth is within legal limits. 

An obviously under-inflated tyre is likely to cause the car to fail its MOT. 

You can also fail your MOT if the car's tyre pressure monitoring system (TPMS) is showing as faulty.

What is Bar?

Bar is a measurement unit mainly used in countries that use the metric system. The UK tends to use a mixture of metric and imperial units, hence the confusion.

1 Bar is a metric unit of pressure, used in everything from measuring atmospheric pressure to scuba diving oxygen tanks.

What is PSI?

PSI stands for pounds per square inch. It’s a also a unit of pressure used by countries that live by the imperial measurement system – and it’s also used in the UK by many people.

As the name suggests, it measures the amount of force applied to one square inch of surface area. Both Bar and PSI are usually quoted in most car owners manuals when referring to tyre pressure.

How many PSI in 1 Bar?

1 Bar is the equivalent to 14.5 PSI – or 14.5038 PSI to be specific.

How to convert Bar to PSI

A simple conversion to convert Bar to PSI is to multiply the pressure value in Bar by 14.5038.

So if your tyre pressure measures 2 Bar, you’ll calculate: 2 x 14.0538 = 29.01 PSI.

• 2.5 Bar (2.5 x 13.0528) is 36.26 PSI
• 3 Bar (3 x 14.0538) is 43.51 PSI.

How to convert PSI to Bar

To convert PSI to Bar, simply do the previous calculation in reverse.

One bar is equal to 14.5038 PSI.

So, Bar = PSI divided by 14.5038.

For example, to get 30 PSI in Bar, you’ll do the following calculation:

• 30 / 14.5038 = 2.068 Bar.
• 35 PSI = 2.413 Bar
• 40 PSI = 2.757 Bar