# Convection Heat Transfer Calculator

> Find the convective heat flow between a surface and the surrounding air or liquid from the heat transfer coefficient, area and temperature difference.

Category: Science & engineering · Applies to: Worldwide · Last updated: 2026-10-29
Interactive calculator: https://calculators.geekmidst.com/calculators/convection-heat-transfer-calculator

Convective heat flow is Q̇ = hA(T_s − T_∞). The hard part is the coefficient h, which depends on the fluid and how fast it moves; typical ranges are given below.

Also called: Newton’s law of cooling calculator, Convective heat loss calculator.

## Inputs
- Heat transfer coefficient (h) (unit W/(m²·K); default 25)
- Surface area (unit m²; default 2)
- Surface temperature (unit °C; default 80)
- Fluid temperature (away from the surface) (unit °C; default 20)

## Results
- Heat flow from the surface
- Heat flux
- Convective resistance 1 ÷ (hA)
- Direction

## Formula

```
Q̇ = h × A × (T_s − T_∞);  R_conv = 1 ÷ (h × A)
```

Where:
- h: convective heat transfer coefficient
- A: surface area in contact with the fluid
- T_s: surface temperature
- T_∞: bulk fluid temperature

## Worked example
1. ΔT = 80 − 20 = 60 K.
2. Q̇ = 25 × 2 × 60 = 3000 W (1500 W/m²).
3. R_conv = 1 ÷ (25 × 2) = 0.02 K/W.

**Result:** A 2 m² surface at 80 °C in moving air at 20 °C with h = 25 W/(m²·K) loses about 3 kW by convection.

## What the result means

A positive result is heat leaving the surface. Hot surfaces also lose heat by radiation, which can be similar in size for still air, so add the Stefan–Boltzmann result for a total.

## Assumptions and limits
- h is uniform over the surface and known.
- Temperatures are steady.
- h is an estimate unless taken from a correlation (Nusselt number) for your geometry and flow; results are only as good as h.

## Questions

### How do I get a better value of h?

Use a Nusselt-number correlation for your geometry (flat plate, pipe, cylinder) with the Reynolds or Rayleigh number, or measured data.

### Is this the same as Newton’s law of cooling?

Yes. Newton’s law of cooling states that the convective heat loss is proportional to the temperature difference, with h as the constant.

## Related calculators
- [Conduction Heat Flow Calculator](https://calculators.geekmidst.com/calculators/conduction-heat-flow-calculator)
- [Stefan–Boltzmann Radiation Calculator](https://calculators.geekmidst.com/calculators/radiation-stefan-boltzmann-calculator)
- [Heat Capacity Calculator](https://calculators.geekmidst.com/calculators/heat-capacity-calculator)

Source: GM¹X CalcVerse — https://calculators.geekmidst.com/calculators/convection-heat-transfer-calculator