🔥 Heat Transfer Calculator (Conduction & Convection)

Switch between conduction (Q=kAΔT/L) and convection (Q=hAΔT) heat transfer via tabs. Leave one variable blank in each tab and the rest are calculated automatically.

Enter 4 of heat transfer rate (Q), thermal conductivity (k), area (A), temperature difference (ΔT), and thickness (L), and the remaining one is calculated.

Material Preset (Thermal Conductivity k)

Heat Transfer Rate (Q) (W)

Thermal Conductivity (k) (W/(m·K))

Cross-Section Area (A) (m²)

Temperature Difference (ΔT) (K (or °C))

Thickness/Length (L) (m)

Result

—

Material	Thermal Conductivity k (W/(m·K))
Copper	401
Aluminum	237
Steel	50
Concrete	1.7
Glass	0.8
Water	0.6
Brick	0.6
Wood	0.12
Fiberglass insulation	0.04
Air	0.026

Note: k values are typical textbook reference values (actual values vary with purity, temperature, and manufacturing).

GUIDE

Learn more

Conduction Heat Transfer Formula (Q=kAΔT/L)

Conduction is heat transfer within a material via molecular vibration. Applying Fourier's law of heat conduction to a steady-state 1D plane wall gives:

Q = k × A × ΔT ÷ L

Heat transfer rate (Q) increases with higher thermal conductivity (k), larger area (A) and temperature difference (ΔT), and thinner thickness (L). Used in wall insulation design, heat sink design, and more.

Convection Heat Transfer Formula (Q=hAΔT)

Convection is heat transfer between a solid surface and a moving fluid (air, water, etc.), expressed by Newton's law of cooling.

Q = h × A × ΔT

The convection coefficient (h) varies widely with fluid type and flow regime (natural vs. forced convection). Typical ranges: natural convection in air 5-25, forced convection in air 10-500, forced convection in water 500-10,000 W/(m²·K) — these are representative textbook ranges, not exact values.

Conduction vs. Convection

Conduction transfers heat through molecular vibration within a solid (or stationary fluid), while convection involves physical fluid motion. A real wall loses heat via conduction internally and convection at its surfaces, forming a combined system — this calculator lets you estimate each stage separately.

Frequently asked questions

Why does conduction need 4 values and convection only 3?

The conduction formula (Q=kAΔT/L) has 5 variables (Q, k, A, ΔT, L), while the convection formula (Q=hAΔT) has 4 (Q, h, A, ΔT). With one variable unknown, each formula determines it uniquely, so 4 and 3 values respectively must be provided.

Should I enter ΔT in °C or K?

A temperature *difference* is numerically the same in Celsius and Kelvin (e.g. a 5°C difference equals a 5K difference), so either unit works — just make sure you enter the difference between two points, not an absolute temperature like 300K.

Where do the material k preset values come from?

They are representative room-temperature approximations from common heat transfer engineering textbooks (e.g. Cengel's Heat and Mass Transfer). Actual materials vary by purity, temperature, and manufacturing — consult manufacturer datasheets for precise design work.