Convert coefficient of thermal expansion between 1/K, 1/°C, 1/°F and ppm.
Heat • 6 units
All 6 units on the Thermal Expansion Converter are defined against the per Kelvin (1/K), so each result is one conversion factor away from a single reference rather than the end of a chain of roundings.
The conversion this page is most often opened for is ready before you type anything: 1 1/K = 0.555555556 1/°F. Change either side and every row in the table recalculates with it.
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Two rows in this table are numerically identical to a third: parts per million per kelvin and micrometres per metre per kelvin are the same quantity written two ways, and both are simply 10⁻⁶ of the base unit. That is why datasheets move between ppm/K and µm/(m·K) without comment. Applied to real dimensions the numbers stop looking small — a 30-metre aluminium curtain-wall run at 23 ppm/K moves about 48 mm across a 70 K annual temperature swing, which is why the joints exist.
In most failures it is the mismatch between two coefficients, not the magnitude of either, that does the damage. Glass-to-metal seals rely on alloys such as Kovar precisely because its expansion is engineered to track borosilicate glass; solder joints under large packages crack because the die and the board expand at different rates through every thermal cycle. Circuit-board laminate makes the point sharply: FR-4 expands modestly in-plane but several times faster through its thickness, and above its glass-transition temperature that through-thickness movement is what pulls plated through-holes apart.
The coefficient is itself a function of temperature, which limits how far a single figure can be stretched. Published values state the range they were measured over — commonly something like 20–100 °C — and materials behave quite differently outside it, with many metals contracting proportionally less as they approach cryogenic temperatures. Using a room-temperature coefficient for a furnace fixture or a cryogenic assembly produces a movement estimate that is confidently wrong in a predictable direction.
Quick reference — 1 per Kelvin (1/K) is equal to:
| per Degree Celsius | 1/°C | 1 |
| per Degree Fahrenheit | 1/°F | 0.555555556 |
| ppm per Kelvin | ppm/K | 1,000,000 |
| ppm per °C | ppm/°C | 1,000,000 |
| µm/(m·K) | µm/(m·K) | 1,000,000 |
6 units of thermal expansion, each a fixed multiple of the 1/K. The table spans 1,800,000:1, from ppm/K (0.000001 1/K) to 1/°F (1.8 1/K). Conversion is one multiplication into the base unit and one division out of it, with no lookup table and no approximation.
value_to = value_from × (factor_from ÷ factor_to)1 1/K = 1 1/K1 1/°C = 1 1/K1 1/°F = 1.8 1/K1 ppm/K = 0.000001 1/K1 ppm/°C = 0.000001 1/K1 µm/(m·K) = 0.000001 1/Kwhere:
Assumptions: Factors are exact definitions. Full double precision is carried internally and rounding is applied only for display.
Result25 1/K = 13.8889 1/°F
The coefficient of thermal expansion is the fractional change in length per degree, so its unit is simply reciprocal temperature (1/K). Structural steel sits near 12 × 10⁻⁶ /K, aluminium around 23 × 10⁻⁶, and borosilicate glass near 3 × 10⁻⁶ — which is precisely why laboratory glassware survives thermal shock that would shatter ordinary glass.
The numbers look negligible until they are multiplied by real dimensions. A 10-metre steel span warming by 50 K grows 6 mm, which is more than enough to buckle a rigidly fixed member or bind a machine slide. Because the coefficient is a per-degree interval, values in 1/K and 1/°C are numerically identical, but the imperial 1/°F is smaller by a factor of 1.8 — a conversion worth getting right.