# Thermal Diffusivity Calculator

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

> The thermal diffusivity calculator finds how quickly heat spreads through a material from its thermal conductivity, density and specific heat, with values for common materials.

## Inputs

- Material
- Thermal conductivity k (W/(m·K), BTU/(h·ft·°F))
- Density ρ (kg/m³, g/cm³, g/mL, lb/ft³, lb/in³)
- Specific heat c_p (J/(kg·K), kJ/(kg·K), J/(g·K), BTU/(lb·°F), cal/(g·°C))

## Results

- Thermal diffusivity α
- Time for heat to penetrate 1 cm (≈ L²/α)

## Formula

```
α = k / (ρ·c_p)
```

## Explanation

Thermal diffusivity combines how well a material conducts heat with how much heat it stores. Metals have high diffusivity and feel cold to the touch; wood has low diffusivity and feels warm.

### How to use the Thermal Diffusivity Calculator

- **Material**
- **Thermal conductivity k**
- **Density ρ**
- **Specific heat c_p**

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

### How it works

Choose a material or enter its properties.

### 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 enterMaterialChoose one: Copper, Aluminium, Carbon steel, Stainless steel …Thermal conductivity kUnits: W/(m·K), BTU/(h·ft·°F)Density ρUnits: kg/m³, g/cm³, g/mL, lb/ft³, lb/in³Specific heat c_pUnits: J/(kg·K), kJ/(kg·K), J/(g·K), BTU/(lb·°F), cal/(g·°C)

### What each result means

- **Thermal diffusivity α** = [k]÷([rho]×[cp])
- **Time for heat to penetrate 1 cm (≈ L²/α)** = 1e-4÷[Thermal diffusivity α]

### 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))Thermal diffusivity α (mm²/s)0.5116.24540.75116.24541116.24541.25116.24541.5116.24542116.2454

## Worked example

Inputs — Material: Copper.

Results — **Thermal diffusivity α = 116.24536 mm²/s**; Time for heat to penetrate 1 cm (≈ L²/α) = 0.8602 s.

## Key terms

- **Thermal diffusivity**: Rate of temperature spreading, k/(ρc_p).

## FAQ

**Why does metal feel colder than wood?**
Its high diffusivity draws heat from your hand quickly.

**What is the diffusivity of water?**
About 0.14 mm²/s.

**How is it used?**
In transient heat problems – cooking times, quenching, building thermal mass.

**What units does it have?**
m²/s, like kinematic viscosity.

**What formula does the Thermal Diffusivity Calculator use?**
α = k / (ρ·c_p).


## 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/)