How to Convert PSIG to PSIA

By John Woloch
Psia includes the weight of the atmosphere; psig does not.

When you check the pressure on the front tire of your bicycle, the dial of your gauge will show the calculated psi (pounds per square inch), such as 85 psi. The pressure inside your tire is not 85 pounds per square inch, however. Your pressure gauge is measuring the difference between the pressure in your bicycle tire and atmospheric pressure. The pressure in your tire actually is 85 pounds per square inch above atmospheric pressure. This type of pressure measurement is pounds per square inch gauge (psig). Scientists and engineers use another unit, pounds per square inch actual (psia), for pressure measurements that include atmospheric pressure.

Write the value in pounds per square inch gauge (psig) you want to analyze. For example, write "17 psig."

Add 14.7 to the value you have written. For example, if the gauge registers 17 psi, 17 + 14.7 = 31.7.

Write your answer using the correct units. For example, write "31.7 pounds per square inch actual (psia).

About the Author

John Woloch writes professionally for various websites. He has published in the Dutch journal "Crux" and writes frequently on oil painting, classical languages and topics involving math and biochemistry. Woloch holds a Master of Arts in English from the University of Chicago, a Master of Arts in classics from Ohio State University and a postbaccalaureate pre-medical degree from Georgetown University.