Psig To Psia Converter
Convert pressure between gauge pressure (PSIG) and absolute pressure (PSIA) by accounting for atmospheric pressure.
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Understanding Gauge vs. Absolute Pressure (PSIG vs. PSIA)
In the world of pressure measurement, you'll often encounter two related but distinct terms: PSIG and PSIA. Understanding the difference is crucial for accurate measurements in engineering, automotive, and scientific applications.
What is PSIG (Gauge Pressure)?
PSIG stands for "Pounds per Square Inch Gauge." This is the pressure measurement most of us are familiar with. It measures the pressure of a system relative to the surrounding atmospheric pressure.
- When a tire pressure gauge reads 32 PSIG, it means the pressure inside the tire is 32 PSI higher than the atmospheric pressure outside the tire.
- If a system is open to the atmosphere, its gauge pressure is 0 PSIG.
- A vacuum or negative pressure would be represented as a negative PSIG value.
What is PSIA (Absolute Pressure)?
PSIA stands for "Pounds per Square Inch Absolute." This measurement is relative to a perfect vacuum (zero pressure). It is the sum of the gauge pressure and the current atmospheric pressure.
PSIA = PSIG + Atmospheric Pressure
The Conversion Formula
To convert between PSIG and PSIA, you need to know the atmospheric pressure. For standardization, a value for standard atmospheric pressure at sea level is used:
Standard Atmospheric Pressure ≈ 14.7 psi
Our calculator uses a more precise value of 14.696 psi.
- PSIG to PSIA:
PSIA = PSIG + 14.696 - PSIA to PSIG:
PSIG = PSIA - 14.696
Practical Example
A car tire is inflated to 32 PSIG at sea level. What is its absolute pressure?
PSIA = 32 PSIG + 14.696 = 46.696 PSIA
This means the total pressure inside the tire is 46.696 pounds per square inch relative to a perfect vacuum.
Frequently Asked Questions (FAQ)
- Why are there two types of pressure measurement?
- Gauge pressure (PSIG) is practical for many applications because it tells you the pressure difference relative to your immediate surroundings. For example, it tells you how much a tire is inflated above the air around it. Absolute pressure (PSIA) is crucial in scientific and engineering contexts where total pressure is important, such as in thermodynamics (e.g., gas laws) or when dealing with vacuums.
- Is my tire pressure gauge measuring PSIG or PSIA?
- Almost all standard pressure gauges, including tire gauges, measure in PSIG. They are designed to read zero when open to the air.
- Does atmospheric pressure change?
- Yes, atmospheric pressure changes with altitude and weather conditions. For precise conversions, you would use the actual local atmospheric pressure instead of the standard 14.696 psi. However, for most general purposes, the standard value is sufficient.
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