Tyre Pressure Units PSI to Bar to kPa

Have you ever wondered why tyre pressure is not measured the same way around the world? There are three different types of measurements used around the world for tyre pressure, from PSI to Bar to kPa. To find out more about these tyre pressure measure systems, read on and find out how to convert from one to the others whenever needed.

Checkout our Tyre Pressure Charts for popular car models.

History and Meaning of kPa

The kPa equals to 1000 Pascals and it is a metric unit used to measure pressure. Pascals owe their name to Blaise Pascal, a French scientist who was particularly interested in measuring the strength needed in diverse hydraulic systems. Pascals are quite a small unit mostly used to measure low pressure environments, and that’s why tyre pressure is commonly measured in kPa in countries which follow the metric system (think kilometres and kilograms instead of miles and pounds).

It is commonly used in most of Europe, except for Britain where the imperial system is way more commonly used. It is widely accepted as more reputable than the Bar, for reasons which we will discuss in further detail along this article.
In mathematics and science, the Pascals and kPa are well more used than Bars, however, in countries which use the imperial system, kPa are converted to PSI.

Pascals measure pressure by unit area, and since Newtons (which get their name from Sir Isaac Newton) measure applied strength for the metric system, both are often correlated. A Pascal means one Newton per square meter.

The Pascal is still the most commonly used means of measurement for pressure in scientific contexts, even in countries which use the imperial system, so scientists often have to convert PSI to Pascals. This results from its invention coming from a well-known scientist, so it is a given in the scientific community that when you are talking about pressure in an article, youâ€™ll measure it in Pascals.

History and Meaning of Bar

Bars are also related to Pascals, in that a Bar equals to one hundred thousand Pascals. Bars were firstly invented as a measure means by the Norwegian meteorologist Vilhelm Bjerknes. It is a metric unit of pressure, and it’s most commonly used in weather forecasting (since Bjerknes is considered to be the founding father of modern weather forecasting). However, due to the bad reputation meteorology gets as a science, Bars are not commonly used in science. Its name derives from the Greek word baros, which means weight. The Bar is a metric measure unit, however, it is not conventionally accepted by the International System of Units (SI), which regulates metric system units.

Since Pascals are a quite small unit, milibars are more commonly used for weather forecasting to measure atmospheric pressure. A milibar equals to 101.325 kPa. For convenience, milibars are used in meteorology since Pascals would return much larger values, which are difficult to deal with when talking about weather forecasting. Milibars solve this issue and even though they are not accepted within the International System of Units, they are still used commonly around most of the world. This includes Europe and most Asian countries, which are known to use the metric system as well.

History and Meaning of PSI

A PSI translates to a pound-force per square inch, and is the most commonly used pressure unit among countries which use the imperial system, like the United States of America, Britain (where the imperial system was first implemented) and other countries like Liberia and Myanmar.

The PSI originates from the avoirdupois pound, which was part of the avoirdupois system that England was known to have used ever since the fourteenth century. Its history begins with the wool trade: an avoirdupois pound was a pound of wool. It was only in 1959 that the avoirdupois pound was standardised and became a unit used around the world for the imperial system. The avoirdupois was the predecessor of the common known pound that is still used in the modern world for the imperial system, which can be a headache if you have to convert PSI to kPa or Bars. This happens especially when you live in a country that uses the imperial system, like the United States, and you buy a car from Europe that is not standardised to imperial measurement units.

Either kPa, PSI or Bar can be used to measure tyre pressure depending on the country, so it is a nightmare for amateur mechanics (and some professionals as well if they are only used to one type of measurement, be it according to the metric or the imperial system). If you ever need to make that type of conversion, read on to figure out the formulas used.

How to convert Bars to PSI

If you’re using a car that uses bars to measure its tyre pressure, you have to know that one bar equals to 14.503773773 PSI. This makes for quite difficult calculations to do if you want to be precise. Let’s say you have a car that needs 2.5 bar of tyre pressure and you need to know how much that means in PSI.

So you multiply 2.5 per 14.503773773 and you get approximately 36,26 PSI. This is an average tyre pressure requirement, but all cars have different tyre pressure requirements to keep your tyres running for a longer time.

How to convert PSI to Bars

If, on the other hand, you’re from a country that uses the metric system and you just got an American car, you have to do the opposite math – convert PSI to Bars. One PSI equals to 0.0689475729 Bar, so if you have a car that requires 30 PSI for tyre pressure you multiply thirty per 0.0689475729 and you get around 2.07 Bars.

How to convert PSI to kPa

Now that you know that one Bar equals to 100000 Pascals, and one kPa equals to 1000 Pascals, the math is a bit easier on this one. To know the exact tyre pressure in kPa, you get the 30 PSI from the example above and you multiply them by 0.0689475729, just like before – except this time you’ll have to multiply the 2.07 per one hundred, which gives you 207 kPa in tyre pressure. Not so difficult anymore, is it?

Remember that you should always check your car manual to figure out the required tyre pressure for the specific brand and model you have. Now that you know how to convert between Bars, PSI and kPa, you’ll be able to set the exact tyre pressure your new car needs no matter the measurement your tools are in.

Conversion Chart

PSI	BAR	KPA
1	0.068	6.8
2	0.13	13
3	0.20	20
4	0.27	27
5	0.34	34
6	0.41	41
7	0.48	48
8	0.55	55
9	0.62	62
10	0.68	68
11	0.75	75
12	0.82	82
13	0.89	89
14	0.96	96
15	1.03	103
16	1.10	110
17	1.17	117
18	1.24	124
19	1.31	131
20	1.37	137
21	1.44	144
22	1.51	151
23	1.58	158
24	1.65	165
25	1.72	172
26	1.79	179
27	1.86	186
28	1.93	193
29	1.99	199
30	2.06	206
31	2.13	213
32	2.20	220
33	2.27	227
34	2.34	234
35	2.41	241
36	2.48	248
37	2.55	255
38	2.62	262
39	2.68	268
40	2.75	275
41	2.82	282
42	2.89	289
43	2.96	296
44	3.03	303
45	3.10	310
46	3.17	317
47	3.24	324
48	3.30	330
49	3.37	337
50	3.44	344
51	3.51	351
52	3.58	358
53	3.65	365
54	3.72	372
55	3.79	379
56	3.86	386
57	3.93	393
58	3.99	399
59	4.06	406
60	4.13	413
61	4.20	420
62	4.27	427
63	4.34	434
64	4.41	441
65	4.48	448
66	4.55	455
67	4.61	461
68	4.68	468
69	4.75	475
70	4.82	482
71	4.89	489
72	4.96	496
73	5.03	503
74	5.10	510
75	5.17	517
76	5.24	524
77	5.30	530
78	5.37	537
79	5.44	544
80	5.51	551
81	5.58	558
82	5.65	565
83	5.72	572
84	5.79	579
85	5.86	586
86	5.92	592
87	5.99	599
88	6.06	606
89	6.13	613
90	6.20	620
91	6.27	627
92	6.34	634
93	6.41	641
94	6.48	648
95	6.55	655
96	6.61	661
97	6.68	668
98	6.75	675
99	6.82	682
100	6.89	689