Thermal Expansion Converter
Convert between thermal expansion coefficient units — per Kelvin, per Celsius, per Fahrenheit, and more — instantly. Real-time conversion with copy-to-clipboard.
Thermal Expansion Converter
Enter a value in any unit — see the conversion in all others instantly.
How to Use the Thermal Expansion Converter
An engineering textbook lists the linear expansion coefficient of aluminium as 23 x 10 to the minus 6 per Kelvin. Your project spec sheet requires the value in per degrees Celsius. The numbers are identical because the degree sizes match — but if the spec requires per Fahrenheit, you need to multiply by 1.8. Enter the coefficient, pick the source unit, and see the converted values in all four scales.
A 50-metre steel bridge expands as temperature changes. The structural spec provides the coefficient as 12 x 10 to the minus 6 per degree C. Enter 0.000012 in per Celsius and the converter shows the same value in per Kelvin, plus 0.00000667 in per Fahrenheit. The per Fahrenheit value is smaller because each Fahrenheit degree represents a smaller temperature change.
A polymer datasheet lists the volumetric expansion coefficient as 200 x 10 to the minus 6 per Kelvin. You need the value per Fahrenheit for a US client. Enter 0.0002 in per Kelvin and the result shows 0.0001111 in per Fahrenheit. The conversion factor is exactly 5/9 because Fahrenheit degrees are 5/9 the size of Kelvin degrees.
Invar alloy has a linear expansion coefficient of approximately 1.2 x 10 to the minus 6 per Kelvin — extremely low for precision optics. Enter 0.0000012 in per Kelvin and the converter shows the equivalent in all four scales. The per Rankine value is identical to the per Fahrenheit value because Rankine and Fahrenheit share the same degree size.
A copper pipe with a linear coefficient of 17 x 10 to the minus 6 per degree C runs 20 metres. Over a 50 degree C temperature range it expands by 17 millimetres. Enter 0.000017 in per Celsius and the converter confirms the same value per Kelvin, which you can use directly in the expansion loop calculation.
How the Thermal Expansion Converter Works
The converter translates thermal expansion coefficients between four temperature scales using multiplicative ratios. All calculations run in your browser with no server dependency.
Coefficient Types
Thermal expansion describes how materials change size with temperature. The linear expansion coefficient (alpha) measures fractional change in length per degree. The area expansion coefficient (beta) is roughly 2 alpha and applies to surfaces. The volumetric expansion coefficient (gamma) is roughly 3 alpha and applies to three-dimensional bodies. For isotropic materials, beta equals 2 alpha and gamma equals 3 alpha. The unit conversion is the same regardless of which type you are working with.
Scale-to-Scale Conversion Factors
Celsius and Kelvin share the same degree size, so 1 per degree C equals 1 per Kelvin exactly. Fahrenheit and Rankine degrees are smaller by a factor of 5/9, which means 1 per degree F equals 1.8 per Kelvin. The converter multiplies the input by the ratio of source-to-target factors. For example, converting 23 x 10 to the minus 6 per K to per degree F gives 23 / 1.8 = 12.78 x 10 to the minus 6 per degree F.
Reference Values for Common Materials
Typical linear expansion coefficients: aluminium approximately 23 x 10 to the minus 6 per K, steel approximately 12 x 10 to the minus 6 per K, copper approximately 17 x 10 to the minus 6 per K, concrete approximately 12 x 10 to the minus 6 per K, and common plastics 50 to 200 x 10 to the minus 6 per K. Materials like Invar have extremely low coefficients near 1.2 x 10 to the minus 6 per K for precision applications such as clock mechanisms and scientific instruments.
Frequently Asked Questions
What is the difference between linear and volumetric thermal expansion?
Linear expansion (α) measures the fractional change in length per degree, while volumetric expansion (γ) measures the fractional change in volume per degree. For isotropic materials, γ is approximately three times α. Use linear for rods or beams, and volumetric for liquids, gases, or three-dimensional solids.
What is the typical thermal expansion coefficient of steel?
The linear coefficient for most structural steels is approximately 12 × 10⁻⁶ per Kelvin (12 µm/m·°C). This means a 1-meter steel bar expands by about 0.012 mm for each degree Celsius temperature increase.
Why is 1/°C equal to 1/K?
The Celsius and Kelvin scales have identical degree sizes — they differ only in their zero points. Since thermal expansion is about the change in temperature rather than absolute temperature, the offset is irrelevant. A 1°C change equals a 1 K change, so 1/°C = 1/K.
How does temperature range affect thermal expansion?
The coefficient of thermal expansion is not perfectly constant — it can vary with temperature. Most published values are averages over a common range (e.g., 20–100°C). For precise engineering over wide temperature ranges, temperature-dependent CTE data should be used.
Which materials have the highest thermal expansion?
Polymers and plastics typically have the highest CTEs, ranging from 50 to 200 × 10⁻⁶ 1/K. Among metals, aluminum (≈ 23 × 10⁻⁶ 1/K) and copper (≈ 17 × 10⁻⁶ 1/K) expand more than steel. Ceramics and Invar alloys have very low expansion for precision applications.
Why does thermal expansion matter in engineering?
Uncontrolled thermal expansion can cause structural stress, warping, or failure in bridges, rails, pipes, and electronic assemblies. Engineers account for expansion using joints, expansion loops, or materials with low CTE to prevent damage from temperature changes.