Is the Thermal Conductivity Converter free?

Yes, Thermal Conductivity Converter is totally free :)

Can I use the Thermal Conductivity Converter offline?

Yes, you can install the webapp as PWA.

Is it safe to use Thermal Conductivity Converter?

Yes, any data related to Thermal Conductivity Converter only stored in your browser (if storage required). You can simply clear browser cache to clear all the stored data. We do not store any data on server.

What is thermal conductivity and what does it measure?

Thermal conductivity (symbol λ or k) quantifies how efficiently a material transfers heat. It is defined as the rate of heat flow per unit area per unit temperature gradient. A high value means heat travels easily through the material (e.g., copper at 385 W/(m·K)); a low value means the material resists heat flow (e.g., aerogel at 0.015 W/(m·K)).

How does this thermal conductivity converter work?

All conversions use W/(m·K) as the normalised base unit. The input value is first multiplied by the source unit's conversion factor to obtain the equivalent in W/(m·K), then divided by the target unit's conversion factor to reach the final result. This two-step method ensures accuracy for any combination of the ten supported units.

What is the difference between W/(m·K) and BTU/(h·ft·°F)?

Both measure thermal conductivity but use different unit systems. W/(m·K) is the SI standard used in science and most of the world, while BTU/(h·ft·°F) is the conventional imperial unit common in US building codes, HVAC, and construction. 1 W/(m·K) ≈ 0.5779 BTU/(h·ft·°F), or equivalently, 1 BTU/(h·ft·°F) ≈ 1.731 W/(m·K).

What are the material presets and how accurate are they?

The material presets provide standard reference values for 30+ common materials — metals, insulation, polymers, gases, and liquids — at approximately 25 °C. These are accepted textbook values (NIST, ASHRAE, engineering handbooks). Thermal conductivity varies with temperature and microstructure, so treat preset values as typical references rather than exact specifications.

Can thermal conductivity be a negative number?

No. Thermal conductivity is always a non-negative physical quantity. A value of 0 W/(m·K) would represent a perfect insulator (a theoretical limit). This tool rejects negative inputs and accepts 0 as a valid edge case.

What precision should I use for my calculations?

For most engineering work, 4–6 significant figures are sufficient. Conversion factors are stored to 10 significant figures, and JavaScript double-precision arithmetic provides approximately 15 significant digits. For very small values (such as aerogels ~0.015 W/(m·K)) or high-conductivity materials (diamond ~2,200 W/(m·K)), the tool automatically switches to scientific notation to avoid misleading rounding.

Thermal Conductivity Converter

Thermal Conductivity Converter – W/(m·K), BTU/(h·ft·°F) and More

The Thermal Conductivity Converter is a free online tool that instantly converts thermal conductivity values between ten standard units used in materials science, mechanical engineering, building physics, HVAC design, and scientific research. Whether you need to convert SI values in W/(m·K) to imperial BTU/(h·ft·°F) for a US construction project, or translate CGS cal/(s·cm·°C) to modern SI for a scientific paper, this tool delivers accurate results in real time with an optional all-units reference table and a library of 30+ material presets.

All conversions are computed entirely in the browser using W/(m·K) as the normalised base unit. No sign-up or installation is required, and results update automatically as you type.

What Is Thermal Conductivity?

Thermal conductivity (symbol λ or k) quantifies a material's intrinsic ability to transfer heat by conduction. It is defined by Fourier's Law of heat conduction:

Q = −λ · A · (ΔT / Δx)

where Q is the heat transfer rate (W), A is the cross-sectional area (m²), ΔT is the temperature difference (K or °C), and Δx is the thickness (m). A high thermal conductivity means heat travels rapidly through the material; a low value means the material resists heat flow and is a good insulator.

Thermal conductivity differs from thermal resistance (R-value), which depends on thickness, and from thermal diffusivity, which also accounts for the material's heat capacity. Thermal conductivity is a pure material property, independent of geometry.

Supported Thermal Conductivity Units

SI and Scaled SI Units

W/(m·K) — The SI unit of thermal conductivity and the global scientific standard. Equal to 1 watt of heat flux per metre of thickness per kelvin of temperature difference.
mW/(m·K) — One thousandth of W/(m·K). Used for gases and highly insulating materials such as aerogels (~15 mW/(m·K)) and air (~26 mW/(m·K)).
kW/(m·K) — One thousand W/(m·K). Convenient for expressing very high conductors such as diamond (~2,200 W/(m·K) = 2.2 kW/(m·K)).
W/(cm·K) — 1 W/(cm·K) = 100 W/(m·K). Common in semiconductor and thin-film thermal management literature.

Imperial / US Units

W/(in·K) — 1 W/(in·K) ≈ 39.37 W/(m·K). Used in US electronic and PCB thermal design where board dimensions are given in inches.
BTU/(h·ft·°F) — The standard imperial unit for thermal conductivity in US building codes, HVAC, and construction. 1 BTU/(h·ft·°F) ≈ 1.731 W/(m·K). ASHRAE and US building standards use this unit extensively.
BTU·in/(h·ft²·°F) — Used in the US for expressing insulation material conductivity, closely related to the R-value per inch. 1 BTU·in/(h·ft²·°F) ≈ 0.1442 W/(m·K).
BTU/(s·ft·°F) — A high-flux imperial unit. 1 BTU/(s·ft·°F) ≈ 6,230 W/(m·K). Encountered in rapid transient heat transfer calculations.

CGS and Practical Metric Units

cal/(s·cm·°C) — The CGS unit. 1 cal/(s·cm·°C) = 418.68 W/(m·K). Found in older scientific literature, especially in geophysics, geology, and pre-SI chemistry texts.
kcal/(h·m·°C) — A practical metric unit used in food science, process engineering, and older European technical standards. 1 kcal/(h·m·°C) ≈ 1.163 W/(m·K).

How Thermal Conductivity Conversion Works

Every conversion normalises through W/(m·K) in two steps. First, the input value is multiplied by the source unit's conversion factor to obtain the equivalent in W/(m·K). Then that value is divided by the target unit's conversion factor to produce the result.

Example — converting 1 W/(m·K) to BTU/(h·ft·°F):

1 W/(m·K) × 1 [already in base] = 1 W/(m·K)
1 W/(m·K) ÷ 1.7307 [BTU/(h·ft·°F) factor] = 0.5779 BTU/(h·ft·°F)

Example — converting 385 W/(m·K) (copper) to BTU/(h·ft·°F):

385 W/(m·K) ÷ 1.7307 = 222.5 BTU/(h·ft·°F)

Thermal conductivity and temperature

Thermal conductivity is not constant — it changes with temperature. The values shown in the material presets are approximate values at around 25 °C. For precision engineering work, consult material datasheets at the relevant operating temperature.

Typical Thermal Conductivity Values by Category

Aerogel: ~0.015 W/(m·K) — one of the best solid insulators
Glass wool / rock wool: ~0.04 W/(m·K) — common building insulation
Air: ~0.026 W/(m·K) — gas-phase insulation baseline
Concrete: ~1.4 W/(m·K) — structural material
Glass: ~1.0 W/(m·K) — moderate conductor
Stainless steel: ~16 W/(m·K) — common structural metal
Iron: ~80 W/(m·K) — general metal
Aluminium: ~237 W/(m·K) — excellent lightweight conductor
Copper: ~385 W/(m·K) — best common engineering conductor
Diamond: ~2,200 W/(m·K) — highest known solid conductor

Practical Applications

Building and construction: Building codes in the US use BTU/(h·ft·°F) while international standards use W/(m·K). Architects and engineers frequently need to convert between these systems when comparing specifications or collaborating internationally.
Electronics cooling: Thermal interface materials, heat sinks, and PCB substrates are characterised in W/(m·K) (global) or W/(in·K) (US design tools). Converting accurately ensures thermal management systems perform as specified.
Materials selection: Engineers comparing datasheets from different countries or eras may encounter W/(m·K), BTU/(h·ft·°F), or cal/(s·cm·°C). The material preset library helps identify where a candidate material falls on the conductivity spectrum.
Academic and research use: Physics and chemistry papers may use SI or CGS units depending on era and discipline. This converter handles all common combinations, including the CGS cal/(s·cm·°C) unit found in legacy geophysics and thermodynamics texts.
HVAC and insulation design: Specifying wall, roof, and floor assemblies requires comparing the thermal conductivity of insulation, masonry, and framing materials — often sourced from manufacturers using different unit conventions.

Tips for Using the Thermal Conductivity Converter

Use the Material Preset dropdown to auto-fill known reference values for 30+ materials — grouped by metals, insulation, polymers, gases, and liquids. This is the fastest way to check a typical conductivity in any unit.
Enable Show all unit conversions to display the input value simultaneously in all ten units, organised by measurement system. Ideal for cross-referencing datasheets from different countries or standards bodies.
Use the Swap button to instantly reverse the conversion direction, for example to verify that a W/(m·K) to BTU/(h·ft·°F) result round-trips back to the original value.
The Material Classifier automatically labels your input as Insulator, Low Conductor, or Conductor based on the equivalent W/(m·K) value, providing immediate engineering context for the number.