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Convert Thermal Expansion Units

Material datasheets quote CTE as 1/K, 1/°C, or ppm/°C. Switch those inverse-temperature scales here for alloys, polymers, and composites.

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Frequently Asked Questions

What is the SI unit of thermal expansion (CTE)?

The SI unit of the linear thermal-expansion coefficient is reciprocal kelvin (1/K). For temperature differences, 1/K equals 1/°C. Material datasheets often list the same CTE as ppm/°C instead of the SI thermal-expansion unit; this hub converts those lab and handbook scales back to 1/K.

How do I convert ppm/°C to 1/K?

Divide ppm/°C by 1,000,000: 1 ppm/°C = 0.000001 1/K. Open our ppm/°C to 1/K converter when a steel or polymer datasheet uses parts per million per degree Celsius and your model expects SI CTE units.

Are 1/K and 1/°C the same for thermal expansion?

Yes for temperature differences: a one-kelvin change equals a one-degree-Celsius change, so a CTE in 1/K equals the same number in 1/°C. Do not treat 1/°F as identical—one kelvin is 1.8 Fahrenheit degrees, so 1 (1/°F) = 1.8 (1/K).

Where can I convert 1/K to 1/°C quickly?

Open our 1/K to ppm/°C converter for a focused thermal-expansion pair. Enter reciprocal kelvin and the page returns parts per million per degree Celsius—useful when a CAD library uses 1/K and a steel datasheet prints ppm/°C.

How accurate are thermal expansion conversions on iConverters?

Thermal expansion results use standard defined relationships and calculate locally in your browser. Values align with references used in materials handbooks, ASME piping guides, and structural expansion-joint documentation. No account is required, and visible answers on this thermal-expansion hub feed structured FAQ data.

What is the SI thermal expansion unit?

The SI thermal expansion unit is reciprocal kelvin (1/K). The linear coefficient of thermal expansion (CTE, α) is the fractional change in length per kelvin. For temperature differences, 1/K equals 1/°C. Steel around 12 ppm/°C is 0.000012 1/K.

Do not confuse CTE with thermal conductivity (W/(m·K)), which measures heat flow, not size change. This hub converts inverse-temperature CTE scales used on material datasheets, piping specs, and CAD libraries.

Common CTE units and conversion factors

Use this factor table to convert common thermal-expansion units to 1/K. 1 (1/°C) = 1 (1/K). 1 (1/°F) = 1.8 (1/K). 1 ppm/°C = 0.000001 1/K. 1 ppm/K = 0.000001 1/K. 1 ppm/°F = 0.0000018 1/K. 1 µε/°C equals 1 ppm/°C.

Alloy handbooks and civil expansion-joint sheets usually print ppm/°C. SI models and many European piping reports use 1/K or 1/°C. US suppliers may quote 1/°F. Enter any of these units in the calculator above instead of multiplying by hand.

Linear, area, and volumetric expansion

Linear CTE (1/K) is the usual datasheet number. Area expansion is about twice the linear coefficient; volumetric expansion is about three times, for isotropic solids. This converter handles the linear inverse-temperature units; apply the 2× or 3× factor only when a report explicitly wants area or volume change.

A 1 m bar with α = 12 ppm/°C grows by 12 µm when temperature rises 1 °C. That is the same as 12 × 10⁻⁶ 1/K. Keep the temperature interval and the length in consistent units when you size expansion joints or pipe loops.

Where each thermal expansion unit is used

ppm/°C dominates metals, polymers, and electronics CTE tables. 1/K and 1/°C appear in SI material cards and finite-element inputs. 1/°F still appears on some US mill certificates. Microstrain-per-degree (µε/K, µε/°C) is the same family as ppm per degree.

ASTM E228, ISO 11359, and ASME piping guides describe how CTE is measured and reported. Quote the temperature range: α is not perfectly constant from cryogenic to annealing temperatures.