How to use this calculator
Pick a typical situation to fill in the convection coefficient h (or enter your own), then the surface area and the surface and fluid temperatures.
Formulas
Newton’s law of coolingQ = hA(Ts − T∞)
Convection resistanceRconv = 1hA
Worked example
2 m² surface at 60 °C in still 20 °C air (the default)
- ΔT = 60 − 20 = 40 K.
- Q = 10 × 2 × 40 = 800 W.
- q″ = 400 W/m²; Rconv = 1/(10 × 2) = 0.05 K/W.
Frequently asked questions
How do I find h?
From correlations for the Nusselt number, Nu = hL/k, which depend on the Reynolds and Prandtl numbers for your geometry. The presets give typical ranges for quick estimates.
Should I add radiation?
For hot surfaces in still air, yes: radiation is often as large as natural convection. Use the radiation calculator and add the two.