One bar contains approximately 1.0197 kilograms of force per square centimeter, which in household calculations and tire pumping is often rounded to 1 kg/cm2 for simplicity. This minimum difference of 2% is critical for fine-tuning industrial hydraulics or gauge gauges, but is virtually invisible when checking tire pressure by a regular driver. Understanding the exact ratio of these values avoids errors when using equipment with different scales, especially when imported devices show PSI or bars, and domestic standards require metric values.
The need to translate units arises every time you come across a heterogeneous technical documentation or toolkit. Technical atmosphereThe bar, which is actually equal to 1 kg/cm2, was historically used in the USSR and is still found in old pressure gauges and GOSTs, whereas the bar is an international unit accepted in most modern cars and compressors. Confusion between these concepts can lead to under-production or over-pumping of systems, which affects the life of the equipment and the safety of operation.
For most practical tasks, such as swapping wheels before a trip, a simplified one-to-one ratio can be used. However, if you are doing a precise setup fuel-system When you are in a diesel engine or check the pressure in the HBO circuit, a more accurate conversion factor is required. In this article, we will analyze the physical basis of units of measurement, give detailed tables and consider the nuances that will help you interpret the readings of the instruments correctly.
Physical essence of units of pressure measurement
Pressure is defined as the force perpendicular to the surface divided by the area of that surface. In the SI system, the basic unit is Pascal, but in technology it is too small, so multiples are used. The bar was introduced for convenience and equals 100,000 Pascals, which is close to atmospheric pressure at sea level. Kilogram force per square centimeter (kgf/cm2) is a unit from the ICGSS system, which is based on gravity acting on a mass of 1 kg.
The difference between these values lies in the standards. Technical atmosphere (a) strictly corresponds to the pressure of a column of water 10 meters high under normal conditions, whereas the bar is tied to the metric system without direct dependence on gravity at a particular location. That is why 1 bar is slightly less than 1 kgf / cm2. When working with high-precision pneumatic systems Ignoring this difference can lead to an accumulation of error.
- ⚙️ Bar - an extra-systemic unit equal to 10^5 Pa, is widely used in meteorology and technology.
- 🏋️ Kgf/cm2 – The pressure produced by a force of 1 kgf per 1 cm2 area is often referred to as the technical atmosphere.
- 🌍 Physical atmosphere (atm) is an extrasystemic unit equal to 101,325 Pa, different from the technical atmosphere (atm).
⚠️ Note: Do not confuse the technical atmosphere (1 kgf/cm2) with the physical atmosphere (atm). The physical atmosphere is about 3% larger than the technical atmosphere and equals 1.033 kgf/cm2, which is important when working with gas equipment.
The exact formula of translation and the mathematics of the process
To obtain the exact value, a conversion factor derived from the force ratio should be used. One bar is equal to 105 Pascals, and one technical atmosphere (1 kgf/cm2) is equal to 98,066.5 Pascals. Dividing these values, we get an exact coefficient: 1 bar = 1.019716 kgf / cm2. In the opposite direction, the formula looks like this: 1 kgf / cm2 = 0.980665 bar.
When performing calculations in the mind or quickly assessing the situation, drivers often use the one-to-one rule. This is acceptable because the error is less than 2%, which is usually within the accuracy of cheap pressure gauges. However, if you are programming pressure-controller or adjust the gearbox, it is better to use full values or at least a factor of 1.02 for greater accuracy.
Why is there confusion with the units?
Historically, different countries have used different standards. In Europe, they loved bars and atmospheres, in the USA – PSI, and in the USSR, they approved the technical atmosphere. It took decades to reach a common denominator, but the habit of using “kg” instead of “bar” remained with many old-school mechanics.
The use of a calculator or tables is necessary when high accuracy is required. For example, when adjusting the pressure of injection in Common Rail A difference of 0.05 bar can change the nature of the engine. Therefore, engineers always operate with accurate numbers, avoiding rounding during the design and initial configuration phase.
Comparative table of pressure values
For quick orientation in values, it is convenient to use a summary table. It will help to instantly convert the readings of your gauge into the desired number system without complex calculations. Below are the basic ratios for common values.
| Bar (bar) | Kgs/cm2 (at) | Pascal (Pa) | PSI (pound/inch2) |
|---|---|---|---|
| 1.0 | 1.02 | 100 000 | 14.50 |
| 1.5 | 1.53 | 150 000 | 21.75 |
| 2.0 | 2.04 | 200 000 | 29.00 |
| 2.5 | 2.55 | 250 000 | 36.25 |
| 3.0 | 3.06 | 300 000 | 43.50 |
As can be seen from the table, with increasing pressure, the absolute error in rounding increases. If at 1 bar the difference is about 0.02 kgf/cm2, then at 10 bars it will already reach 0.2 kgf/cm2. This can be significant for systems operating at their limits, for example, in the air suspension heavy trucks or industrial compressors.
Applications in the automotive and tyre industries
In automotive theme, the question "how much in 1 bar kg / cm2" arises most often when pumping tires. Car manufacturers indicate the recommended pressure in stickers on door racks or in the gas tank hatch using different designations. European stamps are often written in bars, and the instructions may be indicated in kgf / cm2. Compressors can have a double scale or only one.
For passenger cars, the standard pressure is the range from 2.0 to 2.5 bar (kgf/cm2). In this range, the difference between the units of measurement is only 0.04-0.05 units, which is visually impossible to notice on a hand gauge. Therefore, if the instruction requires 2.2 kgf/cm2 and you have pumped 2.2 bar, the difference will be insignificant for everyday driving.
- 🚗 For passenger cars, a difference of 0.1 bar is not critical for safety.
- 🚛 For dual-stowered trucks, accuracy is more important because of the heavy axle load.
- 🏎️ In sports and racing, pressure is measured to within a hundredths using digital pressure gauges.
However, you should be careful when using gas distribution equipment (GBO). The pressure in the evaporator reducer can be adjusted in increments of 0.1-0.2 bar, and it is already important to understand what scale you are torque. An error in the setting can lead to improper operation of the engine on gas or increased fuel consumption.
⚠️ Always check the pressure in cold tires. After the trip, the pressure rises due to the heating of the air, and the readings will be incorrect, regardless of the unit chosen.
Features of working with hydraulics and pneumatics
In hydraulic systems, pressure can reach hundreds or even thousands of bars. The use of a simplified ratio of 1:1 is no longer acceptable. Hydraulic presses, lifts and braking systems require accurate compliance with the parameters specified in the equipment passport. Excess pressure even by 5% can lead to rupture of hoses or failure of seals.
Pneumatic systems that work with compressed air are also sensitive to settings. Pneumatic tools, such as wagons or spray guns, have an optimal range of operation. If the pressure is too high, the tool may wear out quickly or not work properly. Pressure reducers Often have a scale in bars, while old gauges on receivers have an atmosphere.
☑️ Checking system pressure
Service slug-suspension If you make a mistake in the units of measurement when pumping air into cylinders, the system may not properly work out the unevenness of the road, which will lead to discomfort and accelerated wear of the chassis.
Measurement tools and errors
The accuracy of the unit translation directly depends on the quality of the measuring instrument. Cheap mechanical pressure gauges often have an error of up to 10%, which completely covers the difference between bar and kgf/cm2. In such cases, it is simply pointless to bother with an exact coefficient of 1.0197. Digital devices show data more accurately, but they also require periodic calibration.
When choosing a tool, pay attention to the accuracy class. For garage use, class 2.5 or 4.0 is enough, where the dividing price allows you to see tenths of a unit. For professional work with fuel-equipment We need to have sample gauges with accuracy class 0.6 or 1.0 that will show the difference between the measurement systems.
- 🔧 Mechanical pressure gauges are reliable, but are afraid of vibration and hydraulic shocks.
- 📱 Digital sensors are more accurate, but require power and are temperature sensitive.
- 📉 The error of the instrument often exceeds the difference between the bar and the atmosphere.
Tip: If your gauge only shows PSI and you need bars, divide the value by 14.5. This will give a fairly accurate result for household needs.
It is also important to consider the temperature coefficient of expansion of a liquid or gas in the measurement system. In the cold, the readings may differ from summer values. Therefore, the reference pressure is always reduced to a temperature of 20°C. If you measure the pressure of hot oil in an engine or a heated tire, adjust for the temperature or wait for cooling.
Frequently Asked Questions (FAQ)
Is 1 bar equal to 1 atmosphere?
In the home, yes, you can. The difference is only about 1.3%, which does not affect the tires pumping or the operation of most household appliances. However, in exact engineering and science, these are different quantities: 1 bar = 0.9869 atm (physical atmosphere).
What is the difference between kgf/cm2 and kg/cm2?
Formally, kgf/cm2 means kilogram-force per centimeter square, which is the correct unit of pressure. The recording of kg/cm2 is often used as a shorthand, but physically a kilogram is a unit of mass, not a unit of force. In the context of pressure, it is force that is meant.
Why is the compressor on two scales?
Two scales (usually bar/atm and PSI) are plotted for the convenience of users from different regions and with different equipment. This allows you to use one device for maintenance of equipment of both European and American production without recalculations.
How to quickly transfer PSI to bars?
For quick translation, divide the PSI by 14.5. For example, 30 PSI is divided by 14.5, we get about 2.07 bar. To translate back, multiply the bars by 14.5.
Does altitude affect readings?
Absolute pressure varies with altitude, but pressure gauges usually show excess pressure (the difference with atmospheric pressure). Therefore, the gauge readings in the tire on the mountain and by the sea will be the same at the same temperature if the system is sealed.
For a car and household 1 bar is 1 kg / cm2. For precision engineering, use a factor of 1.0197.