Iron Thermal expansion (25 °C) 11.8 µm·m−1·K−1 In plain English, that is saying "the thermal expansion of iron at 25°C is 11.8 micro meters per meter [of material diameter or thickness] per degree Kelvin [or per Kelvin in current terminology] of temperature difference." " 11.8 µm·m−1·K−1 " should be written " 11.8 µm · m−1 · K−1 " or " 11.8 µm / m / K " I can't explain why you get a different value than "they" do because I can't tell what values you are using for the distance (m in meters) and the temperature difference K (in Kelvins.) It's all multiplication and division, no addition or subtraction involved. Sample: At 50°C, what would the increase in length of a piece of iron that is 10m long at 25°C be? The formula for figuring this would be ΔL = Coeffthermal expansion Fe * L * ΔT So L = 10m and ΔT = 50 - 25 = 25K (so there is some subtraction) So the thermal expansion (ΔL) = 11.8µm/m/K · 10m · 25K = 2950µm (or 2.95mm), note that both m and K cancel out.
