Have you ever encountered a situation where the pressure gauge shows pressure at bars, and the instructions for the car or spare parts indicate the values in kg/cm²? This confusion over units of measurement can lead to serious errors, from incorrect tire pressure to brake failure. Car repair shops and garages still use both systems, so the ability to quickly and accurately convert bar in kg/cm² (and vice versa) is a must-have skill for any car owner or mechanic.
In this article we will not just give a ready-made formula, but will analyze why is the conversion factor 1.0197 and not the rounded 1.02 or 1.0, as is often mistakenly believed. You will learn where in the car it is critical to maintain translation accuracy (spoiler: these are hydraulic systems and fuel lines), and where an error of 1-2% can be allowed. We have also collected current correspondence tables for popular pressure values in passenger and truck tires, brake circuits and even air conditioning systems.
Why are bar and kg/cm² different units of the same value?
Let's start with the basics: bar and kg/cm² (kilogram-force per square centimeter) - both units measure pressure, but originated in different systems:
- 🔹 Bar — a metric unit adopted in the international SI system. 1 bar ≈ atmospheric pressure at sea level. Widely used in Europe and modern technical documents.
- 🔹 kg/cm² (aka technical atmosphere, designation
at) is an old engineering unit that came from the MKGSS system. Popular in the USSR and is still found in domestic manuals, especially for older car models (for example, VAZ 2107 or GAZ-53).
The key difference is the basis of the calculation: bar is related to pascals (1 bar = 100,000 Pa), and kg/cm² is related to the force of gravity of a standard kilogram acting on an area of 1 cm². Because of this, their ratio is not circular, but equal 1.0197. Many generally take 1 bar ≈ 1 kg/cm², but in critical systems (for example, in power steering or diesel fuel rail) such an error can lead to breakdowns.
Formula for converting bar to kg/cm² and reverse calculation
Basic formula for conversion:
1 bar = 1.0197162129779 kg/cm²
1 kg/cm² = 0.980665 bar
In practice, simplified coefficients are used:
- 🔢 For quick conversion bar → kg/cm²: multiply the value by
1.02(error ~0.2%). - 🔢 For reverse conversion kg/cm² → bar: multiply by
0.98(error ~0.07%).
Examples of calculations:
| Bar | kg/cm² (kgf/cm²) | Example of application in a car |
|---|---|---|
| 2.0 | 2.0394 | Car tire pressure (winter mode) |
| 8.5 | 8.6676 | Truck brake system KAMAZ |
| 0.3 | 0.3059 | High pressure fuel pump (injection pump) in idle mode |
| 150 | 152.957 | Hydraulic press for suspension repair |
For accurate calculations (for example, when setting Common Rail diesel) use the full factor of 1.0197. For everyday use (tires, brakes) 1.02 is sufficient.
Where in a car is translation accuracy important?
Not all vehicle systems are equally sensitive to unit conversion errors. Let's consider the critical areas:
⚠️ Attention: B fuel systems of diesel engines (especially with Common Rail) a pressure deviation of 0.1 bar can lead to unstable engine operation or even failure of the injectors. Always use the exact odds of 1.0197!
- ⚙️ Fuel system: Rail pressure Common Rail reaches 1800–2500 bar. An error of 1% here is equal to 18–25 bar, which is critical for the operation of the injectors.
- 🚗 Brake system: In hydraulic brakes of passenger cars, the working pressure is 80–120 kg/cm² (78–117 bar). An error of 2–3 kg/cm² will worsen the braking distance.
- 🔧 Hydraulic tools: Jacks, presses and pullers operate at 50–300 bar. Inaccurate translation can lead to thread failure or deformation of parts.
- ❄️ Air conditioning system: Freon pressure is measured in bars (for example, 2.8 bar for R134a), but in old manuals it may be indicated in kg/cm².
Where can you not bother with accuracy? B tires an error of 0.1–0.2 bar (1–2%) has virtually no effect on controllability. For example, if 2.2 bar is recommended, and you pumped up 2.25 bar (2.29 kg/cm² instead of 2.24 kg/cm²), this is acceptable.
Why did they use kg/cm² in the USSR?
This unit was convenient for engineering calculations, as it was directly related to weight. For example, a pressure of 1 kg/cm² means that for every square centimeter of the surface there is a force equal to the weight of 1 kg. This is intuitive for mechanics working with loads and hydraulics.
Conversion table for car owners
To avoid counting every time, save this table with popular values:
| Bar | kg/cm² (kgf/cm²) | PSI | Application |
|---|---|---|---|
| 0.5 | 0.510 | 7.25 | Minimum bicycle tire pressure |
| 1.8 | 1.836 | 26.1 | Summer tire pressure sedan (for example, Toyota Corolla) |
| 2.4 | 2.447 | 34.8 | Winter tire pressure crossover (for example, Kia Sportage) |
| 3.0 | 3.059 | 43.5 | Truck tires ZIL-130 (front axle) |
| 8.0 | 8.158 | 116.0 | Brake system GAZelle Next |
| 15.0 | 15.296 | 217.6 | Hydraulic power steering MAZ |
Please note: the table also shows values in PSI (pounds per square inch) is an American unit often found on imported compressor gauges. To convert PSI to kg/cm², divide the value by 14.223.
Common translation mistakes
Even experienced mechanics sometimes make mistakes. Here are the most common mistakes:
⚠️ Attention: Never be confused kg/cm² with kPa (kilopascals)! 1 kg/cm² ≈ 98.066 kPa. The error here can be 100 times! For example, 2 kg/cm² = 196 kPa, not 2 kPa.
- ❌ Round up to 1:1. Many people believe that 1 bar = 1 kg/cm². This is only true as a rough estimate. For example, at a pressure of 100 bar the error will be 2 kg/cm²!
- ❌ Ignoring temperature. Pressure in closed systems (e.g. hydraulic accumulator) depends on temperature. When heated by 10°C, the pressure will increase by ~0.1 bar.
- ❌ Failure to take into account altitude. At an altitude of 1000 m, atmospheric pressure drops by ~0.1 bar. This is important when tuning fuel systems.
- ❌ Transfer via PSI. Some people first convert bar to PSI (1 bar ≈ 14.504 PSI), and then PSI to kg/cm², which adds extra error.
How to avoid mistakes? Use direct translation through coefficient 1.0197 or proven online calculators (for example, on the websites Bosch or Mannol).
☑️ Checking the accuracy of the translation
Online calculators and mobile applications
If you need to quickly convert bar to kg/cm², use these tools:
- 📱 Applications:
- 🔧 Unit Converter (Android/iOS) - supports 50+ pressure units.
- 🚗 Auto Doctor — a specialized converter for cars (includes PSI, kPa, kg/cm²).
- 💻 Online services:
- 🔗 Convert-me.com — accurate translation with payment history.
- 🔗 RapidTables — correspondence tables for car services.
When choosing a calculator, pay attention to:
- Coefficient accuracy (should be 1.0197, not 1.02).
- Availability of additional units (PSI, kPa, atm).
- The ability to save frequently used values (for example, the tire pressure of your car).
For professional work (service station, diagnostics), use calculators with support dynamic pressure — they take into account changes in parameters during movement or heating.
Practical examples for motorists
Let's look at real situations where unit conversion is needed:
Example 1: Inflating tires.
In the instructions for Hyundai Solaris the indicated pressure is 2.3 bar. Your compressor displays values in kg/cm². What should I do?
2.3 bar × 1.0197 ≈ 2.345 kg/cm²
Set the pressure gauge to 2.35 kg/cm².
Example 2: Checking the brake system.
After replacing the brake hoses with Ford Transit you need to check the pressure in the circuit. The manual requires 100 kg/cm², and your tester shows in bars:
100 kg/cm² ÷ 1.0197 ≈ 98.07 bar
Acceptable range: 95–100 bar.
Example 3: Common Rail diagnostics.
When scanning Bosch KTS showed fuel rail pressure of 350 bar. In the specification Mercedes OM642 the minimum value indicated is 355 kg/cm². Is the pressure normal?
350 bar × 1.0197 ≈ 356.9 kg/cm²
356.9 > 355 → pressure is normal.
The last example shows how important accuracy is: if rounded to 1.02, the result would be 357 kg/cm², which is also within normal limits, but in borderline cases (for example, 348 bar) an error could lead to a false conclusion about a malfunction.
FAQ: Frequently asked questions about converting bar to kg/cm²
Is it possible to use a rounded factor of 1.02 for tires?
Yes, a 2% error is acceptable for car and truck tires. For example, at the recommended 2.2 bar:
- Exact calculation: 2.2 × 1.0197 ≈ 2.243 kg/cm².
- Rounded: 2.2 × 1.02 ≈ 2.244 kg/cm².
The difference of 0.001 kg/cm² is imperceptible. However, for sports cars (for example, Porsche 911) it is better to stick to exact values.
Why do tire pressure gauges often not have a scale in kg/cm²?
Manufacturers are guided by international standards, where the main units are bar and PSI. Kg/cm² remained mainly in post-Soviet countries and China. If your pressure gauge only shows PSI, use double translation:
1 kg/cm² ≈ 14.223 PSI
Example: 2.5 kg/cm² = 2.5 × 14.223 ≈ 35.56 PSI
How to convert kg/cm² to atmospheres (atm)?
Technical atmosphere (at) and kg/cm² are the same thing (1 at = 1 kg/cm²). Physical atmosphere (atm) is different:
1 atm ≈ 1.0332 kg/cm²
1 kg/cm² ≈ 0.9678 atm
In auto repair, technical atmospheres (at) equal to kg/cm² are usually used.
Where else can kg/cm² be found in a car?
In addition to tires and brakes, kg/cm² is indicated in:
- 🔧 Features oil filters (for example, the valve is activated at 1.2 kg/cm²).
- ⚡ Options batteries (electrolyte pressure during charging).
- 🔥 Systems turbocharging (boost pressure in old manuals).
- 🛠️Instructions for hydraulic jacks and the press.
Is it possible to convert bar to kg/cm² via kPa?
Yes, but this is an extra step. First convert bar to kPa (1 bar = 100 kPa), then kPa to kg/cm² (1 kg/cm² ≈ 98.066 kPa):
X bar → X × 100 kPa → (X × 100) ÷ 98.066 ≈ X × 1.0197 kg/cm²As you can see, we get the same coefficient of 1.0197. It's easier to use direct translation.