# Thermal Conductivity Calculator (Heat Flux)

URL: https://speedycalculator.com/calculators/physics/thermal-conductivity/
Last updated: 2026-10-30

> The thermal conductivity calculator finds the heat flux and heat flow through a slab of material from its thermal conductivity, thickness and the temperature difference – or the conductivity from measured flux.

## Inputs

- Find
- Material
- Thermal conductivity k (W/(m·K), BTU/(h·ft·°F))
- Measured heat flux (W/m², kW/m²)
- Temperature difference ΔT (K, °C, °F)
- Thickness Δx (cm, mm, m, in, ft)
- Area (optional) (m², cm², mm², km², in², ft²)

## Results

- Heat flux q″
- Heat flow
- Thermal conductivity k

## Formula

```
q″ = k·ΔT/Δx,  Q̇ = q″·A
```

## Explanation

Thermal conductivity measures how well a material conducts heat: copper about 400 W/(m·K), glass about 1, insulation foam 0.03. Fourier's law turns it into a heat flow through walls, pans and electronics.

### How to use the Thermal Conductivity Calculator

- **Find**
- **Material**
- **Thermal conductivity k**
- **Measured heat flux**
- **Temperature difference ΔT**
- **Thickness Δx**
- **Area (optional)**

Results update as you type, every field has its own unit menu, and everything is calculated in your browser.

### How it works

Choose what to find and enter the values.

### Tips

- Use absolute temperature (K) in gas laws and efficiency formulas.
- Temperature differences are the same in K and °C.
- Heat = mass × specific heat × temperature change when no phase change occurs.
- Phase changes need latent heat at a constant temperature.

### Common mistakes to avoid

- Using °C in pV = nRT.
- Forgetting latent heat during melting or boiling.
- Confusing heat capacity (J/K) with specific heat (J/(kg·K)).

### Inputs explained

FieldWhat to enterFindChoose one: Heat flux, Thermal conductivityMaterialChoose one: Copper, Aluminium, Carbon steel, Stainless steel …Thermal conductivity kUnits: W/(m·K), BTU/(h·ft·°F)Measured heat fluxUnits: W/m², kW/m²Temperature difference ΔTUnits: K, °C, °FThickness ΔxUnits: cm, mm, m, in, ftArea (optional)Units: m², cm², mm², km², in², ft²

### Example values

How the main result changes when **Thermal conductivity k** changes and everything else stays at the example values above:

Thermal conductivity k (W/(m·K))Heat flux q″ (W/m²)0.51440.7514411441.251441.51442144

## Worked example

Inputs — Find: Heat flux; Material: Brick; Temperature difference ΔT: 20 K; Thickness Δx: 10 cm; Area (optional): 1 m².

Results — **Heat flux q″ = 144 W/m²**; Heat flow = 144 W.

## Key terms

- **Heat flux**: Heat flow per unit area.

## FAQ

**Which material conducts heat best?**
Diamond (~2,000 W/(m·K)), then silver and copper.

**Why are gases good insulators?**
Their molecules are far apart.

**What is Fourier's law?**
Heat flux is proportional to the temperature gradient.

**Why do foams insulate well?**
They trap still air in tiny cells.

**What formula does the Thermal Conductivity Calculator use?**
q″ = k·ΔT/Δx,  Q̇ = q″·A.


## Sources

- [Incropera – Fundamentals of Heat and Mass Transfer (reference text)](https://www.wiley.com/en-us/Fundamentals+of+Heat+and+Mass+Transfer%2C+8th+Edition-p-9781119320425)
- [The Engineering ToolBox](https://www.engineeringtoolbox.com/)