Thermal Conductivity Calculator
Calculate heat flux through materials using Fourier law q = λ·ΔT/Δx with material presets for copper, brick, glass, wood, and more. Free online physics heat transfer calculator with charts and breakdowns.
About This Calculator
The Thermal Conductivity Calculator computes heat flux through a material using Fourier's law of heat conduction: q = λ × ΔT / Δx. It supports a built-in database of common materials including metals (copper, silver, gold, aluminum), building materials (brick, glass, wood), insulation materials (urethane foam, glass fibre, soft rubber), and gases (air, helium). You can also enter a custom thermal conductivity value for any material not in the database.
The calculator is designed for students learning heat transfer concepts, engineers designing thermal management systems, architects evaluating building insulation, and anyone needing to compute conductive heat transfer through planar walls. Select a material, enter the temperature difference and thickness, and the calculator instantly returns the heat flux in watts per square meter (W/m²).
Understanding Fourier's Law
Fourier's law of heat conduction states that the rate of heat transfer through a material is proportional to the negative temperature gradient and the area through which heat flows. For one-dimensional steady-state conduction through a flat wall, this simplifies to q = λ × ΔT / Δx, where q is the heat flux (W/m²), λ is the thermal conductivity (W/m·K), ΔT is the temperature difference (K), and Δx is the wall thickness (m).
For example, a brick wall (λ = 0.6 W/m·K) that is 35 cm thick with an indoor temperature of 20°C and outdoor temperature of 0°C (ΔT = 20 K) has a heat flux of 0.6 × 20 / 0.35 = 34.3 W/m². This means every square meter of wall loses 34.3 joules of heat energy per second. Adding insulation reduces heat loss by lowering the effective thermal conductivity.
Applications of Thermal Conductivity
Thermal conductivity values are essential in building design (selecting insulation materials), electronics cooling (choosing heat sink materials), cookware manufacturing (selecting pan materials for even heating), aerospace engineering (thermal protection systems), and HVAC system design (calculating heating and cooling loads). Understanding a material's thermal conductivity helps engineers and architects make informed decisions about energy efficiency and thermal management.
Frequently Asked Questions
What is thermal conductivity?
Thermal conductivity (λ) is a material property that measures how easily heat passes through a material. It is defined as the rate of heat transfer per unit area per unit temperature gradient, with SI units of watts per meter per Kelvin (W/m·K). Materials like copper and diamond have high thermal conductivity, while materials like wood and air have low thermal conductivity.
How does the thermal conductivity calculator work?
This calculator uses Fourier law of heat conduction: q = λ × ΔT / Δx, where q is the heat flux in W/m², λ is the thermal conductivity of the material in W/m·K, ΔT is the temperature difference across the material in Kelvin, and Δx is the thickness of the material in meters. Select a material from the preset list or enter a custom thermal conductivity value, then input the temperature difference and thickness to compute the heat flux.
What is the formula for heat flux?
Heat flux (q) is calculated using Fourier law: q = λ × ΔT / Δx. For example, a brick wall with thermal conductivity 0.6 W/m·K, temperature difference of 20 K, and thickness of 0.35 m gives a heat flux of 0.6 × 20 / 0.35 = 34.29 W/m². This means 34.29 joules of heat energy pass through every square meter of the wall each second.
What materials have high thermal conductivity?
Diamond has the highest thermal conductivity at 2000 W/m·K, followed by silver (429 W/m·K), copper (401 W/m·K), gold (317 W/m·K), and aluminum (237 W/m·K). These materials are excellent heat conductors and are commonly used in heat sinks, cookware, and thermal management applications.
What materials are good thermal insulators?
Materials with low thermal conductivity are good insulators. Rigid urethane foam (0.022 W/m·K), air (0.024 W/m·K), glass fibre (0.04 W/m·K), soft rubber (0.13 W/m·K), and wood (0.17 W/m·K) are effective thermal insulators commonly used in building insulation, packaging, and thermal protection.
What is the difference between thermal conductivity and thermal resistance?
Thermal conductivity (λ) is a material property measuring how well a material conducts heat, while thermal resistance (R) measures how much a specific object resists heat flow. Thermal resistance depends on both the material conductivity and the object geometry: R = Δx / (λ × A) for a flat plate, where Δx is thickness and A is cross-sectional area. The two are reciprocally related for a given geometry.
Why is the heat flux negative in Fourier law?
In Fourier law, the complete equation is q = -λ × dT/dx. The negative sign indicates that heat flows from regions of higher temperature to regions of lower temperature, opposite to the direction of the temperature gradient. This calculator provides the magnitude of heat flux (absolute value), as the direction is understood to be from hot to cold.
How does thickness affect heat transfer through a wall?
Heat flux is inversely proportional to thickness according to Fourier law: q = λ × ΔT / Δx. Doubling the wall thickness halves the heat flux, making thicker walls better insulators. This is why building codes specify minimum insulation thicknesses and why double-glazed windows with an air gap significantly reduce heat loss compared to single-pane windows.