ppm/°F

part per million per Fahrenheit degree

Thermal expansion coefficientexact by definition

The part per million per Fahrenheit degree is exactly 1.8 × 10⁻⁶ /K, because a Fahrenheit degree is 5/9 of a kelvin so a per-Fahrenheit coefficient must be larger by 9/5 to describe the same material. Steel is 6.5 ppm/°F, the same statement as 11.7 ppm/K.

1 ppm/°F 0.0000018 1/K