PSIG to PSIA

Use local atmospheric pressure for precise results.

PSIG to PSIA

Use local atmospheric pressure for precise results.

Precision: 3

PSIG (Gauge pressure)

Gauge pressure relative to ambient air.

PSIA (Absolute pressure)

Absolute pressure referenced to a perfect vacuum.

Atmospheric pressure (P_atm) in psi

Tip: PSIA = PSIG + P_atm.

Quick presets

Formula: PSIA = PSIG + P_atm

How to Convert PSIG to PSIA

Converting PSIG (gauge pressure) to PSIA (absolute pressure) is a straightforward process that involves adding the local atmospheric pressure to your gauge reading. Here's a step-by-step guide:

Measure PSIG Read your gauge

Add P_atm ≈14.7 psi at sea level

Get PSIA Result in absolute

Example Conversion

If your gauge reads 50 PSIG at sea level:

PSIA = 50 + 14.7 = 64.7 PSIA

Important Note

Always use your local atmospheric pressure for accurate results, especially at high altitudes.

PSIG to PSIA Formula

The formulas for converting between PSIG and PSIA are simple and rely on the atmospheric pressure value:

PSIG → PSIA

PSIA = PSIG + P_atm

Add atmospheric pressure to gauge pressure

PSIA → PSIG

PSIG = PSIA − P_atm

Subtract atmospheric pressure from absolute

Where P_atm ≈ 14.6959 psi at sea level (standard atmospheric pressure). This value decreases at higher altitudes.

PSIG to PSIA Conversion Chart

Quick reference table for common PSIG to PSIA conversions at sea level (P_atm = 14.7 psi):

PSIG	PSIA	Common Use
0	14.7	Atmospheric pressure
10	24.7	Low pressure systems
30	44.7	Typical tire pressure
50	64.7	Compressed air tools
100	114.7	Industrial applications
125	139.7	Steam systems
150	164.7	High pressure systems
-14.7	0	Perfect vacuum

Note: These values assume standard sea-level atmospheric pressure. Adjust for local conditions when precision is required.

PSIG and PSIA Difference

Understanding the difference between PSIG and PSIA is crucial for accurate pressure measurements in engineering and scientific applications.

PSIG (Gauge Pressure)

Referenced to local atmospheric pressure
Zero point = ambient air pressure
Can be negative (vacuum)
Used in: tire pressure, air tools, general industry

PSIA (Absolute Pressure)

Referenced to perfect vacuum
Zero point = complete absence of pressure
Always positive (cannot be below zero)
Used in: thermodynamics, altitude calculations, scientific work

PRESSURE SCALE REFERENCE

0 PSIA

Vacuum

14.7 PSIA

Sea Level

= 0 PSIG

Higher

Positive PSIG

PSIG to PSIA Equation

The mathematical relationship between PSIG and PSIA is expressed through a simple linear equation:

P_abs = P_gauge + P_atm

P_abs = Absolute pressure (PSIA)

P_gauge = Gauge pressure (PSIG)

P_atm = Atmospheric pressure

Sea Level

P_atm ≈ 14.696 psi

Denver (5,280 ft)

P_atm ≈ 12.2 psi

Mount Everest

P_atm ≈ 4.4 psi

Is PSI PSIA or PSIG?

"PSI" (pounds per square inch) is the unit of pressure measurement, but it doesn't specify whether it's absolute or gauge. Here's how to determine which type is meant:

PSIG

Gauge reading

Shown on most gauges

PSIA

Absolute reading

Scientific & engineering

PSI

Context dependent

Usually means PSIG

Rule of Thumb

When "PSI" is written without a suffix, it usually means PSIG in practical applications. Always confirm the reference point when precision matters.

PSIG vs PSIA vs PSID

These three pressure measurement types serve different purposes. Here's a comprehensive comparison:

Aspect	PSIG	PSIA	PSID
Full Name	Pounds per Square Inch Gauge	Pounds per Square Inch Absolute	Pounds per Square Inch Differential
Reference Point	Local atmosphere	Perfect vacuum	Another pressure point
Can Be Negative?	Yes (vacuum)	No	Yes
Zero Meaning	Atmospheric pressure	Complete vacuum	No pressure difference
Common Uses	Tires, air tools, HVAC	Thermodynamics, altitude	Filters, flow meters

What is PSID?

PSID measures the pressure difference between two points, such as across a filter or valve. It doesn't reference atmosphere or vacuum—only the delta between two pressures.

PSIG vs PSIA vs PSI

Understanding the relationship between these terms is essential for correctly interpreting pressure measurements:

PSI

The base unit—pounds per square inch. Describes force per area without specifying reference.

PSIG

PSI measured relative to atmospheric pressure. Most common for everyday use.

PSIA

PSI measured from true zero (vacuum). Required for scientific calculations.

PSIA vs PSIG Gauge

Physical pressure gauges can be designed to measure either PSIA or PSIG, and the type you use depends on your application:

PSIG Gauge

✓ Reads 0 at atmospheric pressure
✓ Open to atmosphere on one side of diaphragm
✓ Most common type for industrial use
✓ May show negative values for vacuum

PSIA Gauge

✓ Reads ≈14.7 at atmospheric pressure
✓ Sealed vacuum reference chamber
✓ Used for precise scientific measurements
✓ Always shows positive values

How to Identify Your Gauge Type

Check the gauge face for markings: "G" or "PSIG" indicates gauge pressure, "A" or "PSIA" indicates absolute. If unmarked, assume PSIG—it's the default for most industrial gauges.

Frequently Asked Questions

Is 14.7 PSIA equal to 0 PSIG?

Yes—under sea-level standard conditions, a system at atmospheric pressure reads ≈14.7 PSIA and 0 PSIG.

Are PSIA and PSIG the same?

No. PSIA is absolute (vacuum reference). PSIG is gauge (ambient reference). Use PSIA for thermodynamics and when altitude matters.

What does 14.7 PSIA mean?

It’s the absolute pressure at sea level in standard conditions—air pressing with 14.7 pounds per square inch above vacuum.

Is 14.7 PSIA atmospheric pressure?

It’s the widely used standard reference for sea level. Real atmospheric pressure varies with weather and altitude.

What is 0 PSIG to PSIA?

0 PSIG equals approximately 14.7 PSIA at sea level. This is because PSIA = PSIG + atmospheric pressure. When gauge pressure is zero, absolute pressure equals atmospheric pressure (≈14.7 psi at sea level).

125 PSIG is equivalent to what PSIA?

125 PSIG equals approximately 139.7 PSIA at sea level. Using the formula PSIA = PSIG + P_atm: 125 + 14.7 = 139.7 PSIA. At different altitudes, adjust for local atmospheric pressure.

What is the PSIA if the pressure is 150 PSIG?

At sea level, 150 PSIG equals 164.7 PSIA. Using the conversion formula: PSIA = PSIG + P_atm = 150 + 14.7 = 164.7 PSIA.

Does the conversion from PSIG to PSIA depend on temperature?

The formula itself (PSIA = PSIG + P_atm) doesn't directly depend on temperature. However, atmospheric pressure can vary slightly with temperature changes, which may affect the conversion at extreme conditions.

Are PSIG and PSIA units used worldwide?

PSIG and PSIA are primarily used in the United States and some other countries. Most of the world uses metric units like Pascal (Pa), bar, or kilopascal (kPa) for pressure measurements.

Is PSI equal to PSIG?

Not exactly. PSI is the base unit (pounds per square inch), while PSIG specifically indicates gauge pressure. When PSI is written without a suffix, it usually implies PSIG in practical applications, but you should always verify the reference point.

What is the full form of PSIG?

PSIG stands for Pounds per Square Inch Gauge. It measures pressure relative to the local atmospheric pressure, where 0 PSIG equals atmospheric pressure.

Why is PSIG always lower than PSIA?

PSIG is always lower than PSIA because PSIG is measured relative to atmospheric pressure, while PSIA is measured from absolute zero (perfect vacuum). The difference equals the atmospheric pressure: PSIA = PSIG + P_atm.

What is the unit of atmospheric pressure?

Atmospheric pressure can be expressed in various units: psi (pounds per square inch), atm (atmospheres), bar, Pa (Pascal), mmHg (millimeters of mercury), or inHg (inches of mercury). Standard sea-level atmospheric pressure is approximately 14.7 psi, 1 atm, 1.013 bar, or 101,325 Pa.

What's the difference between gauge pressure and absolute pressure?

Gauge pressure (PSIG) is measured relative to atmospheric pressure—a tire gauge showing 30 PSIG means 30 psi above atmospheric. Absolute pressure (PSIA) is measured from a perfect vacuum—the same tire would read about 44.7 PSIA (30 + 14.7).