Pound-force per square inch

A pound-force per square inch (or psi) is the measurement unit of pressure.

The normal Earth atmospheric pressure is 14.7 psi, which means that a column of air one square inch in area rising from the Earth's surface (at sea level) to space weighs 14.7 pounds.

After the USS Constellation (NCC-1017) was attacked by the planet killer, the atmospheric pressure on the ship was measured at 11 pounds per square inch.

The class F shuttlecraft Galileo had 15 pounds psi of fuel left when it lifted off from Taurus II, which was just enough to make one orbit.