🔬 Heat Transfer Calculator

Heat transfer by conduction is the flow of thermal energy through a material from the hot side to the cold side. Fourier's Law gives the rate: Q = k × A × ΔT / d, where Q is the heat transfer rate (W), k is thermal conductivity (W/m·K), A is the cross-sectional area (m²), ΔT is the temperature difference (K or °C), and d is the material thickness (m). This is the fundamental equation for building insulation, heat sinks, and thermal management.

From home insulation keeping you warm in winter to computer chips needing heat sinks to avoid overheating, conductive heat transfer governs countless engineering challenges. This calculator determines the heat flow through a wall, slab, or plate given the material properties and temperature conditions.

The calculator applies Q = k × A × ΔT / d. Thermal conductivity k varies enormously: metals conduct well (copper: 400 W/m·K), while insulators resist flow (fibreglass: 0.04 W/m·K).

The R-value of insulation is R = d/k—the higher R, the better the insulation. A wall with R-20 allows 20 times less heat flow per unit area than R-1 for the same ΔT.

1. Enter the thermal conductivity (k) in W/(m·K).
2. Enter the surface area (A) in m².
3. Enter the temperature difference (ΔT) in °C or K.
4. Enter the material thickness (d) in metres.
5. Click Calculate to find the heat transfer rate Q in watts.

What is thermal conductivity?

Thermal conductivity (k, in W/(m·K)) measures how readily a material conducts heat. Metals have high k (good conductors); insulation materials have low k (good insulators). Diamond has the highest known k of any bulk material.

How does insulation thickness affect heat transfer?

Q is inversely proportional to thickness: doubling the insulation halves the heat flow. This is why thicker insulation saves energy. The R-value (R = d/k) directly captures this: higher R means better insulation.

What is the difference between conduction, convection, and radiation?

Conduction is heat flow through a solid material (Fourier's Law, this calculator). Convection is heat carried by moving fluids (Newton's Law of Cooling). Radiation is heat emitted as electromagnetic waves (Stefan-Boltzmann Law). Real systems often involve all three simultaneously.

Can I use this for multi-layer walls?

Not directly—this calculator handles a single material layer. For composite walls, sum the thermal resistance of each layer: R_total = d₁/k₁ + d₂/k₂ + ..., then Q = A × ΔT / R_total. Each layer's R = thickness/conductivity.

Why does ΔT use the same value in °C and K?

Because it is a temperature difference, not an absolute temperature. A change of 1°C equals a change of 1 K exactly. Absolute temperatures differ by 273.15 (0°C = 273.15 K), but differences are identical.

What is a U-value?

The U-value (thermal transmittance) is the inverse of total R-value: U = 1/R_total. It measures heat flow per unit area per degree: Q = U × A × ΔT. Lower U means better insulation. Building codes often specify maximum U-values for walls, windows, and roofs.

Use watts (W) for Q, W/(m·K) for k, m² for A, and K (or °C, since only differences matter) for ΔT, and metres for d. Temperature difference ΔT = T_hot − T_cold always gives positive Q (heat flows hot to cold). For composite walls (layers of different materials), sum the thermal resistances: R_total = Σ(dᵢ/kᵢ), then Q = AΔT/R_total. Convection and radiation are separate heat transfer modes not covered by this calculator.