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Thermal Expansion Converter

Science

Convert coefficient of thermal expansion between per-Kelvin, per-Celsius, per-Fahrenheit, and ppm/°C — used for materials science and engineering design.

Reviewed by the thecalcu.com team · Last updated July 21, 2026

From
To
All conversionsfor 1 Parts per Million per °C (ppm/°C)
Per Kelvin (1/K)0.000001
Per Celsius (1/°C)0.000001
Per Fahrenheit (1/°F)5.5556e-7
Per Rankine (1/°R)5.5556e-7
Parts per Million per °C (ppm/°C)1

What is a Thermal Expansion?

The Thermal Expansion Converter converts the coefficient of thermal expansion between per-Kelvin, per-Celsius, per-Fahrenheit, per-Rankine, and the materials-science-standard parts per million per °C (ppm/°C). This coefficient describes how much a material's dimensions change per degree of temperature change, a critical value in engineering design wherever materials experience temperature swings.

Enter a value in any supported unit and the converter calculates the equivalent instantly. For the underlying temperature-scale relationship this conversion depends on, see the Temperature Interval Converter.

Why Use a Thermal Expansion Converter?

Materials datasheets report thermal expansion coefficients in different units depending on the source, SI-based references in per-Kelvin, US engineering references in per-Fahrenheit, and materials science tables commonly in ppm/°C. Comparing CTE values across dissimilar materials for a design decision requires converting them to a consistent unit first, and the ppm-to-fraction and Celsius-to-Fahrenheit scale factors compound in a way that's easy to get wrong manually.

Who Should Use This Converter?

  • Materials engineers comparing thermal expansion coefficients across datasheets that use different unit conventions.
  • Mechanical design engineers working out clearance and stress tolerances for assemblies combining materials with different CTE values.
  • Manufacturing engineers working with international suppliers whose material specs may use per-Fahrenheit or per-Celsius units.
  • Materials science students learning to work with thermal expansion coefficient data across unit systems.

What Insights Does the Thermal Expansion Converter Give You?

The main output is the converted value in your chosen target unit, calculated precisely from the fixed multiplier relationship between units. Because ppm/°C values (typically single or double digits for common materials) look very different in magnitude from raw per-Kelvin fractions (typically in the 10⁻⁵ to 10⁻⁶ range), the converter helps you sanity-check that a value is in the expected range for the unit you're viewing.

How to use this Thermal Expansion calculator

  1. Choose your starting unit from the source dropdown, for example, "Parts per Million per °C (ppm/°C)".
  2. Enter the numeric coefficient value you want to convert in the input field.
  3. Choose your target unit from the destination dropdown, for example, "Per Kelvin (1/K)".
  4. Read the converted result, which updates instantly as you type or change units.
  5. Use the swap (⇅) button if you need to reverse the conversion direction.
  6. Use the copy button to grab the result for a materials comparison or engineering design calculation.
Show formula & methodology ↓Show less ↑

Formula & Methodology

The converter's base unit is per Kelvin (1/K), identical in scale to per-Celsius. Every supported unit has a fixed multiplier:

- 1 per Celsius (1/°C) = 1 per K (identical degree size)
- 1 per Fahrenheit (1/°F) = 1.8 per K (accounts for the smaller Fahrenheit degree size)
- 1 per Rankine (1/°R) = 1.8 per K (identical to per °F)
- 1 ppm/°C = 0.000001 per K

Any conversion follows:

Result = Input × (toBase of source unit ÷ toBase of target unit)

Worked example, converting steel's typical CTE of 12 ppm/°C to per Kelvin:

Result = 12 × 0.000001 = 0.000012 per K (1.2 × 10⁻⁵ /K)

This matches the commonly cited value for steel's linear thermal expansion coefficient in SI units.

Related Tools

You may also find these useful: Thermal Conductivity Converter, CGS to SI Units Converter.

Frequently Asked Questions

What is the coefficient of thermal expansion?
The coefficient of thermal expansion (CTE) measures how much a material's dimensions change per degree of temperature change, expressed in units like per Kelvin (1/K) or parts per million per degree Celsius (ppm/°C). A higher CTE means the material expands or contracts more for a given temperature change.
Why is ppm/°C a common way to express thermal expansion coefficients?
Most solid materials have very small thermal expansion coefficients, a typical metal might expand by only a few thousandths of a percent per degree, so expressing the value in parts per million per °C keeps the numbers in a more readable range than using raw per-Kelvin fractions.
How do I convert ppm/°C to per Kelvin?
Divide the ppm/°C value by 1,000,000, since ppm means 'parts per million.' Enter your value with 'Parts per Million per °C (ppm/°C)' as the source and 'Per Kelvin (1/K)' as the target to apply this automatically.
Why does the per-Fahrenheit unit have a different toBase value than per-Celsius?
Because a Fahrenheit degree interval is smaller than a Celsius/Kelvin interval (5/9 the size), the same physical expansion rate corresponds to a larger 'per °F' value, specifically 1.8 times larger, than the equivalent 'per K' or 'per °C' value, since expansion per smaller degree steps looks like a bigger number per step.
Does this converter account for linear versus volumetric thermal expansion?
No, this converter handles unit conversion of whatever coefficient value you already have; it doesn't distinguish between linear expansion coefficient (length change) and volumetric expansion coefficient (volume change), which are different physical quantities related by roughly a factor of 3 for isotropic materials. Make sure you're comparing coefficients of the same type.
What is a typical thermal expansion coefficient for common materials?
Steel has a CTE of roughly 12 ppm/°C, aluminium roughly 23 ppm/°C, and glass roughly 9 ppm/°C, these differences matter significantly in engineering design where dissimilar materials are joined and need to expand at compatible rates to avoid stress or failure.
Why does thermal expansion coefficient matter in engineering design?
When materials with different thermal expansion coefficients are bonded or fitted together (like a metal fitting in a different metal housing), temperature changes can create mechanical stress or gaps as the materials expand at different rates, engineers need accurate, correctly converted CTE values to predict and design around this.
How does this relate to the Temperature Interval Converter?
Thermal expansion coefficients are defined per unit of temperature interval (not per absolute temperature), so understanding how temperature intervals convert between scales, covered by the [Temperature Interval Converter](/temperature-interval-converter/), is the same underlying logic that determines how thermal expansion coefficients convert between per-Celsius and per-Fahrenheit.
Can this converter be used for both linear and area/volume expansion coefficients?
The unit conversion math works the same regardless of whether you're converting a linear, area, or volumetric expansion coefficient, since the temperature-scale relationship is identical, just be careful not to mix a linear coefficient value with a volumetric one in the same comparison.
How is CTE typically measured in a lab?
CTE is typically measured with a dilatometer, which precisely tracks a sample's dimensional change across a controlled temperature range, then calculates the coefficient from the observed expansion divided by the temperature interval applied.
Also known as
coefficient of thermal expansion converterppm per c to per k convertercte converterthermal expansion coefficient unitslinear expansion coefficient converter