# Overall Heat Transfer Coefficient Calculator (U-value)

URL: https://speedycalculator.com/calculators/physics/heat-transfer-coefficient/
Last updated: 2026-10-30

> The overall heat transfer coefficient calculator finds the U-value and total thermal resistance of a wall of up to four layers, including inside and outside surface convection, and the heat loss for a temperature difference.

## Inputs

- Inside surface coefficient h_i (W/(m²·K), BTU/(h·ft²·°F))
- Outside surface coefficient h_o (W/(m²·K), BTU/(h·ft²·°F))
- Layer 1 thickness (mm, cm, m, in, µm)
- Layer 1 conductivity (W/(m·K), BTU/(h·ft·°F))
- Layer 2 thickness (mm, cm, m, in, µm)
- Layer 2 conductivity (W/(m·K), BTU/(h·ft·°F))
- Layer 3 thickness (mm, cm, m, in, µm)
- Layer 3 conductivity (W/(m·K), BTU/(h·ft·°F))
- Layer 4 thickness (mm, cm, m, in, µm)
- Layer 4 conductivity (W/(m·K), BTU/(h·ft·°F))
- Area (m², cm², mm², km², in², ft²)
- Temperature difference (K, °C, °F)

## Results

- Total thermal resistance
- Overall heat transfer coefficient U
- Heat loss

## Formula

```
R_total = 1/h_i + Σ(t_j/k_j) + 1/h_o,  U = 1/R_total,  q = U·A·ΔT
```

## Explanation

Building regulations limit the U-value of walls, roofs and windows. Each layer adds resistance in series – insulation adds the most per centimetre.

### How to use the Overall Heat Transfer Coefficient Calculator

- **Inside surface coefficient h_i**
- **Outside surface coefficient h_o**
- **Layer 1 thickness**
- **Layer 1 conductivity**
- **Layer 2 thickness**
- **Layer 2 conductivity**
- **Layer 3 thickness**
- **Layer 3 conductivity**
- **Layer 4 thickness**
- **Layer 4 conductivity**
- **Area**
- **Temperature difference**

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

### How it works

Enter the inside and outside surface coefficients, the thickness and conductivity of each layer (thickness 0 = unused), the area and temperature difference.

### 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 enterInside surface coefficient h_iUnits: W/(m²·K), BTU/(h·ft²·°F)Outside surface coefficient h_oUnits: W/(m²·K), BTU/(h·ft²·°F)Layer 1 thicknessUnits: mm, cm, m, in, µmLayer 1 conductivityUnits: W/(m·K), BTU/(h·ft·°F)Layer 2 thicknessUnits: mm, cm, m, in, µmLayer 2 conductivityUnits: W/(m·K), BTU/(h·ft·°F)Layer 3 thicknessUnits: mm, cm, m, in, µmLayer 3 conductivityUnits: W/(m·K), BTU/(h·ft·°F)Layer 4 thicknessUnits: mm, cm, m, in, µmLayer 4 conductivityUnits: W/(m·K), BTU/(h·ft·°F)AreaUnits: m², cm², mm², km², in², ft²Temperature differenceUnits: K, °C, °F

### What each result means

- **Total thermal resistance** = 1÷[Inside surface coefficient h_i] + [Layer 1 thickness]÷[Layer 1 conductivity] + [Layer 2 thickness]÷[Layer 2 conductivity] + [Layer 3 thickness]÷[Layer 3 conductivity] + [Layer 4 thickness]÷[Layer 4 conductivity] + 1÷[Outside surface coefficient h_o]
- **Overall heat transfer coefficient U** = 1÷[Total thermal resistance]
- **Heat loss** = [Area]×[Temperature difference]÷[Total thermal resistance]

### Example values

How the main result changes when **Inside surface coefficient h_i** changes and everything else stays at the example values above:

Inside surface coefficient h_i (W/(m²·K))Overall heat transfer coefficient U (W/(m²·K))3.850.29045.770.29797.690.30189.610.304211.540.305815.380.3078

## Worked example

Inputs — Inside surface coefficient h_i: 7.69 W/(m²·K); Outside surface coefficient h_o: 25 W/(m²·K); Layer 1 thickness: 102 mm; Layer 1 conductivity: 0.72 W/(m·K); Layer 2 thickness: 100 mm; Layer 2 conductivity: 0.035 W/(m·K); Layer 3 thickness: 100 mm; Layer 3 conductivity: 1.4 W/(m·K); Layer 4 thickness: 12.5 mm; Layer 4 conductivity: 0.17 W/(m·K); Area: 20 m²; Temperature difference: 20 K.

Results — Total thermal resistance = 3.31381 m²·K/W; **Overall heat transfer coefficient U = 0.30177 W/(m²·K)**; Heat loss = 120.70711 W.

## Key terms

- **U-value**: Heat flow per area per degree difference.

## FAQ

**What is a good U-value for a wall?**
Below about 0.3 W/(m²·K) in modern buildings.

**Why include surface coefficients?**
Air films at each surface add resistance.

**What is an R-value?**
The total thermal resistance, R = 1/U.

**Does thermal bridging matter?**
Yes – studs and fixings raise the real U-value.

**What formula does the Overall Heat Transfer Coefficient Calculator use?**
R_total = 1/h_i + Σ(t_j/k_j) + 1/h_o,  U = 1/R_total,  q = U·A·ΔT.


## 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/)