On the Job With Joe

Altitude and psig


Follow-up Question on Pressure (psig)

Question: Does altitude make a difference with psig?

Answer: Yes it does. Let me use my tire pressure example (32 psig) again to answer your question. Pound per square inch gauge (psig) is a unit of pressure relative to atmospheric pressure at sea level, which is 14.7. Atmospheric pressure pushes against the earth at 14.7 pounds per square inch at sea level, yet drops to 10.1 pounds per square inch at 10,000 feet. The bottom line is as altitude increases, atmospheric pressure decreases (see table below).
At sea level (14.7), 32 psig in tire is 46.7 psi
At 10,000 feet up in the mountains (10.1), 32 psig in tire is 42.1 psi

Altitude (ft.): Air Pressure (psi)
Sea Level: 14.7
1,000: 14.2
5,000: 12.2
10,000: 10.1