Heat converters
Thermal Expansion Converter
Convert coefficients of thermal expansion between 1/K, 1/°F, ppm/K and µin/(in·°F).
Result
1000000 ppm/K
1 1/K = 1000000 ppm/K
Because a Fahrenheit degree is 5/9 of a kelvin, a coefficient expressed per °F is 1.8 times the same coefficient per kelvin.
All units for this value
| Unit | Symbol | Value |
|---|---|---|
| Per kelvin | 1/K | 1 |
| Per degree Celsius | 1/°C | 1 |
| Parts per million per kelvin | ppm/K | 1000000 |
| Micrometer per meter per kelvin | µm/(m·K) | 1000000 |
| Per degree Fahrenheit | 1/°F | 0.555556 |
| Per degree Rankine | 1/°R | 0.555556 |
| Parts per million per degree Fahrenheit | ppm/°F | 555556 |
| Microinch per inch per degree Fahrenheit | µin/(in·°F) | 555556 |
| Kelvin per unit strain | K | 1 |
About this calculator
Thermal expansion coefficients describe how much a material's size changes per degree of temperature change, a key figure in engineering, construction, and materials science. This converter switches between per-kelvin, parts-per-million-per-kelvin, per-Fahrenheit, and microinch-per-inch-per-Fahrenheit forms of the same underlying property.
How it works in plain English
A coefficient of linear thermal expansion expresses the fractional change in length a material undergoes per degree of temperature change. Because it's a fraction per degree, its numeric value depends entirely on how big the 'degree' in the denominator is. The converter treats per-kelvin as the common anchor and rescales into other forms by adjusting for both the degree size and any multiplier used for readability, such as expressing tiny fractions in parts per million.
Parts-per-million-per-kelvin values are simply the per-kelvin coefficient multiplied by one million, useful because raw coefficients for metals are often numbers like 0.000012, which are easier to read as 12 ppm/K. Fahrenheit-based units follow the same one-fifth-larger-degree relationship seen elsewhere in temperature work: since a Fahrenheit degree is smaller than a kelvin, the same physical expansion corresponds to a coefficient that is 1.8 times larger when expressed per Fahrenheit degree. Microinch-per-inch-per-Fahrenheit is a common US engineering form that expresses the same fractional change using inch-based length units, but it carries the identical numeric value as parts-per-million-per-Fahrenheit.
Select the coefficient's current unit and the unit you want in the from and to menus, type the value, and the converted coefficient appears immediately. A table lists the same coefficient in every supported unit at once, a precision control sets the number of decimal places, and a swap button flips the two chosen units.
The formula
- value_in_target = value_in_source × (source factor to 1/K) ÷ (target factor to 1/K)
- 1 ppm/K = 0.000001 1/K
- 1 (1/°F) = 1.8 (1/K)
- 1 ppm/°F = 1.8 ppm/K
- 1 µin/(in·°F) = 1 ppm/°F = 1.8e-6 1/K
Worked example
Suppose a steel bar has a linear expansion coefficient of 12 ppm/K and you want that expressed per degree Fahrenheit. First convert ppm/K to a plain per-kelvin fraction: 12 × 0.000001 = 0.000012 1/K. Then convert to per-Fahrenheit by dividing by 1.8, since each Fahrenheit degree is smaller than a kelvin: 0.000012 ÷ 1.8 = 0.0000066667 1/°F, or 6.67 ppm/°F.
Entering 12 into the ppm/K field with ppm/°F selected as the target returns 6.67 ppm/°F immediately. The full unit table also confirms this equals 6.67 µin/(in·°F) and 0.0000037 per °F, all calculated from the same starting coefficient without any manual unit juggling.
Typical linear thermal expansion coefficients
| Material | Approx. coefficient (ppm/K) |
|---|---|
| Aluminium | 23 |
| Steel (carbon) | 12 |
| Copper | 17 |
| Glass (soda-lime) | 9 |
| Concrete | 12 |
| Wood (along grain) | 3-5 |
Commonly cited engineering material property values
Frequently asked questions
Why is expansion given in parts per million per kelvin instead of a plain decimal?
Raw thermal expansion coefficients are typically very small decimals, such as 0.000012 for steel, which are easy to misread or mistype. Multiplying by one million turns that into a more manageable number like 12, so parts-per-million-per-kelvin is a common shorthand in engineering tables and datasheets without changing the underlying physical value.
Why does the coefficient change when I switch from per-kelvin to per-Fahrenheit?
The coefficient describes fractional change per degree, and a Fahrenheit degree is a smaller unit of temperature change than a kelvin. Because the same physical expansion is being divided by a smaller number of degrees when using Fahrenheit, the resulting coefficient value is larger by a factor of 1.8 compared to the per-kelvin figure.
Is microinch per inch per °F the same as ppm per °F?
Yes, numerically they're identical. Both express a fractional length change per degree Fahrenheit; microinch-per-inch simply frames that fraction using inch-based length units common in US mechanical engineering, while ppm expresses the same ratio as parts per million. Converting between them involves no scale factor at all.
Does this converter account for volumetric or area expansion?
No, it focuses on linear expansion coefficients, which describe change in one dimension, such as length. Volumetric expansion is often approximated as roughly three times the linear coefficient for isotropic materials, and area expansion as roughly twice, but those approximations aren't applied automatically here.
Why do different materials have such different coefficients?
Expansion behavior depends on how strongly a material's atomic bonds respond to added thermal energy. Metals like aluminium have relatively weak, flexible bonding and expand more per degree, while ceramics like glass have stiffer, more tightly bound structures and expand less. This is why mixing materials with very different coefficients in one structure can create stress as temperature changes.
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