Thermal Conductivity Converter

Convert between W/(m·K), BTU/(h·ft·°F), and cal/(s·cm·°C) — the property that sets how well a material conducts heat, for insulation and engineering.

Thermal Conductivity

W/(m·K), BTU/(h·ft·°F)

From

Result

0.00239

1 W/(m·K) = 0.00239006 cal/(s·cm·K)

Popular conversions

What Is a Thermal Conductivity Converter?

A thermal conductivity converter translates a material's ability to conduct heat between units — watts per metre-kelvin to BTU per hour-foot-Fahrenheit. Thermal conductivity (symbol k or λ) measures how readily heat flows through a material, and the SI unit is W/(m·K). It's the defining property behind insulation R-values, heat-sink materials, and building thermal performance.

This converter routes through W/(m·K). The US building and HVAC industries use BTU/(h·ft·°F), and older references use cal/(s·cm·°C). Values span four orders of magnitude — from ~0.025 W/(m·K) for still air to ~400 W/(m·K) for copper — so accurate conversion is essential when comparing insulators and conductors across systems.

This is one category of the full Unit Converter — pair it with our percentage calculator or scientific calculator for related everyday maths.

How Thermal Conductivity Conversion Works

Everything routes through W/(m·K)

Each unit has a fixed W/(m·K) factor. The converter normalises to it, then projects to BTU/(h·ft·°F) and cal/(s·cm·°C).

k = heat flux × thickness ÷ ΔT

Conductivity links heat flow to a temperature gradient. Higher k means heat passes more easily for the same temperature difference.

Folds power, length, and temperature

Because the unit combines power, length, and a temperature interval, the BTU conversion factor (1.731) reflects all three at once.

Temperature interval, not reading

The kelvin and Fahrenheit here are intervals (per degree of difference), so the 5/9 scaling applies — no +32 offset enters.

Core Thermal Conductivity Conversion Factors

Multiply to reach W/(m·K); divide to come back.

BTU/(h·ft·°F) → W/(m·K)

× 1.730735

One BTU per hour-foot-Fahrenheit is 1.731 W/(m·K). The US-to-SI conductivity bridge.

cal/(s·cm·°C) → W/(m·K)

× 418.4

One calorie per second-centimetre-Celsius is 418.4 W/(m·K) (CGS).

Conductivity (k)

k = q·L / ΔT

Conductivity is heat flux times thickness, divided by the temperature difference.

How to Use the Thermal Conductivity Converter

1
Enter the conductivity value
Type the thermal conductivity you want to convert — a material datasheet value or an insulation spec.
2
Choose the 'from' unit
Pick W/(m·K), BTU/(h·ft·°F), or cal/(s·cm·°C) as your starting unit.
3
Choose the 'to' unit
Select the target unit, or swap the two to reverse direction.
4
Read every unit at once
The all-units table shows the conductivity across W/(m·K) and BTU/(h·ft·°F) together.

Key Thermal Conductivity Concepts

W/(m·K)

The SI unit of thermal conductivity. Copper ~400, steel ~50, water ~0.6, wood ~0.15, still air ~0.025 — a span of four orders of magnitude.

Insulators vs conductors

Low k (foam, air, fibreglass) means a good insulator; high k (metals) means a good conductor. The same property, opposite uses.

R-value connection

Insulation R-value is thickness ÷ conductivity. Converting k correctly is the first step to comparing R-values across unit systems.

Temperature dependence

Conductivity varies with temperature, so datasheet values cite a reference temperature. The unit conversion is separate from that variation.

Real-World Thermal Conductivity Conversions

🏠

Building insulation

Fibreglass is ~0.04 W/(m·K) (0.023 BTU/(h·ft·°F)). Insulation datasheets switch between SI and US units.

🔥

Heat sinks

Aluminium is ~205 W/(m·K), copper ~400. Heat-sink material choice hinges on these conductivity values.

🪟

Glazing

Glass is ~1.0 W/(m·K); the air or argon gap in double glazing is the real insulator at ~0.025–0.018.

🧱

Construction materials

Concrete ~1.7, brick ~0.7, timber ~0.15 W/(m·K). Building thermal models need these in consistent units.

❄️

Cryogenics

Insulation conductivity drops at low temperature. Cryogenic design uses W/(m·K) at the relevant temperature.

💻

Thermal interface

Thermal paste runs ~3–12 W/(m·K). Datasheets quote W/(m·K) to compare pastes and pads.

Best Practices for Thermal Conductivity Conversion

✓Use the 1.731 factor for BTU units. 1 BTU/(h·ft·°F) = 1.731 W/(m·K). It folds power, length, and a temperature interval, so it isn't a round number.
✓Treat the degrees as intervals. The °F and K here are per-degree-of-difference, so only the 5/9 scaling applies — no +32 offset, unlike a temperature reading.
✓Convert k before computing R-value. R-value is thickness ÷ conductivity. Put k in consistent units first, or insulation comparisons across systems will be wrong.
✓Cite the reference temperature. Conductivity changes with temperature. Quote datasheet values at their stated temperature for a meaningful comparison.
✓Know the insulator/conductor scale. Foams and air are ~0.02–0.04 W/(m·K); metals are tens to hundreds. The four-order span helps catch a unit slip.

Common Thermal Conductivity Conversion Mistakes

Adding a +32 offset

The Fahrenheit here is a temperature interval, not a reading. Applying the +32 offset (as for absolute temperature) corrupts the conversion.

Using a round BTU factor

1 BTU/(h·ft·°F) is 1.731 W/(m·K), not 1.7 exactly when precision matters. The folded factor needs care in engineering work.

Confusing conductivity with R-value

Conductivity (k) is a material property; R-value depends on thickness too. They aren't interchangeable, and R-value units differ again.

Ignoring temperature dependence

Comparing conductivities measured at different temperatures, without noting it, misjudges relative insulation performance.

Why Thermal Conductivity Conversion Matters

Thermal conductivity decides which materials insulate a building, cool a chip, or carry heat in a heat exchanger — and it's quoted in W/(m·K) in SI and BTU/(h·ft·°F) in US practice, with a non-round factor that folds power, length, and temperature. Mishandling it, or confusing it with R-value, undermines insulation and thermal-management decisions.

Because the values span four orders of magnitude from air to copper, and because the degrees involved are intervals (so no temperature offset applies), this conversion rewards precision. A converter that routes through W/(m·K) and bridges BTU/(h·ft·°F) lets building scientists and thermal engineers compare material performance reliably across both systems.

Built for building scientists, HVAC and thermal engineers, and materials specialists converting between W/(m·K) and BTU/(h·ft·°F).

Linear unit factors follow the BIPM SI brochure, the NIST Guide to the SI, and ISO 80000. Currency rates load live from open.er-api.com; crypto prices from CoinGecko. See our methodology and editorial policy. Educational only — not certified for regulated trading, settlement, medical, or aerospace use.

Thermal Conductivity Converter FAQs

Divide watts per metre-kelvin by 1.730735 to get BTU per hour-foot-Fahrenheit, or multiply the other way. So fibreglass at 0.04 W/(m·K) is about 0.023 BTU/(h·ft·°F). The factor folds the power, length, and temperature-interval conversions into one.

Thermal conductivity (symbol k or λ) is a material property measuring how readily heat flows through it, in watts per metre-kelvin (W/m·K). High values (copper ~400) mean good conductors; low values (air ~0.025, foam ~0.03) mean good insulators. It's the basis of insulation and heat-sink design.

Because the degrees in a thermal-conductivity unit represent a temperature difference (an interval), not an absolute reading. For intervals, only the size of the degree matters — the 5/9 scaling between Fahrenheit and Celsius/Kelvin — so the +32 offset used for absolute temperatures does not enter the conversion.

R-value (thermal resistance) equals material thickness divided by thermal conductivity: R = L ÷ k. So a thicker or less conductive material has a higher R-value and insulates better. To compare R-values across unit systems, you must first convert the conductivity k consistently — they're related but not the same quantity.

Roughly: copper ~400 W/(m·K), aluminium ~205, steel ~50, glass ~1.0, water ~0.6, wood ~0.15, fibreglass insulation ~0.04, and still air ~0.025. The span of nearly four orders of magnitude between metals and insulators is what makes accurate conversion important when comparing materials.

It uses exact derived factors (1 BTU/(h·ft·°F) = 1.730735 W/(m·K), 1 cal/(s·cm·°C) = 418.4 W/(m·K)) and routes every conversion through W/(m·K) at full precision, so the result is exact to your input precision at the implied reference temperature.