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.
Things You'll Need
- Calculator (optional)
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).
- Texas A&M, Kingsville: Fluid Mechanics
- California State University, Northridge: Cross Connections
- Mississippi State University: Formula Sheet
- "Physics for Scientists & Engineers"; Douglas C.Giancoli; 2008
- Photo Credit David De Lossy/Photodisc/Getty Images
How to Convert Absolute Pressure to Gauge Pressure
Most modern pressure gauges take into account the effect of atmospheric pressure on the systems being measured. Well pumps, air compressors and...
How to Convert PSI into KPa
Units of pressure quantify the perpendicular force pushing against an object, such as the helium in a scuba tank or the force...
How to Convert PSIA to KPA
PSIA (pounds per square inch absolute) is a pressure measurement that assumes a starting point of zero in a perfect vacuum where,...
How to Convert PSI to PSIG
In general, pressure is a force acting on a surface area; the psi unit measures pressure as pounds of force and square...
How to Convert PSIA to ATM
Scientists, meteorologists and others who work with pressure readings use a number of different units. One such unit is the atmosphere (atm)....