μin/(in·°F)

microinch per inch per Fahrenheit degree

Thermal expansion coefficientexact by definition

The microinch per inch per Fahrenheit degree is identical to ppm/°F, exactly 1.8 × 10⁻⁶ /K, written the way US material datasheets write it. The inch over inch is a strain, so the unit is dimensionally the same as the ppm form and only the presentation differs.

Watch out: Also written µin/in/°F or in/in/°F × 10⁻⁶. All three are the same number. The only real risk is dropping the 10⁻⁶ and reading 6.5 as a coefficient rather than 6.5 ppm.

1 μin/(in·°F) 0.0000018 1/K