Heat transfer rate calculator
The rate of heat flow by any of the three mechanisms: conduction through a wall (Q = k·A·ΔT/d), convection from a surface (Q = h·A·ΔT), or radiation between bodies (Q = ε·σ·A·(T₁⁴ − T₂⁴), with temperatures in kelvin). Pick a mode; only its fields matter.
Related tools
All Physics tools →Need Heat transfer rate Q (W), In kilowatts (kW)? The Heat transfer rate calculator derives it from Mechanism, Area A (m²), Temperature 1 — T₁ (°C, or K for radiation), Temperature 2 — T₂ (°C, or K for radiation), Conduction — k (W/m·K), Conduction — thickness d (m), Convection — h (W/m²·K), Radiation — emissivity ε (0–1) in one step. For instance, with Mechanism = Conduction (through a wall), Area A (m²) = 2, Temperature 1 — T₁ (°C, or K for radiation) = 90, Temperature 2 — T₂ (°C, or K for radiation) = 20, Conduction — k (W/m·K) = 0.6, Conduction — thickness d (m) = 0.1, Convection — h (W/m²·K) = 25 and Radiation — emissivity ε (0–1) = 0.9 it returns Heat transfer rate Q (W) = 840 and In kilowatts (kW) = 0.84.
How to use it
- Enter your values: Mechanism, Area A (m²), Temperature 1 — T₁ (°C, or K for radiation), Temperature 2 — T₂ (°C, or K for radiation), Conduction — k (W/m·K), Conduction — thickness d (m), Convection — h (W/m²·K), Radiation — emissivity ε (0–1).
- Read the result instantly: Heat transfer rate Q (W), In kilowatts (kW).
Frequently asked questions
What does the Heat transfer rate calculator actually compute?
It takes Mechanism, Area A (m²), Temperature 1 — T₁ (°C, or K for radiation), Temperature 2 — T₂ (°C, or K for radiation), Conduction — k (W/m·K), Conduction — thickness d (m), Convection — h (W/m²·K) and Radiation — emissivity ε (0–1) and derives Heat transfer rate Q (W) and In kilowatts (kW) from them. The calculation is live as you type, so the result updates on every change.
What information do I need to provide?
8 values: Mechanism, Area A (m²), Temperature 1 — T₁ (°C, or K for radiation), Temperature 2 — T₂ (°C, or K for radiation), Conduction — k (W/m·K), Conduction — thickness d (m), Convection — h (W/m²·K) and Radiation — emissivity ε (0–1). Nothing else is required — no account, no file upload.
Can you show a worked example?
With Mechanism = Conduction (through a wall), Area A (m²) = 2, Temperature 1 — T₁ (°C, or K for radiation) = 90, Temperature 2 — T₂ (°C, or K for radiation) = 20, Conduction — k (W/m·K) = 0.6, Conduction — thickness d (m) = 0.1, Convection — h (W/m²·K) = 25 and Radiation — emissivity ε (0–1) = 0.9, the calculator returns Heat transfer rate Q (W) = 840 and In kilowatts (kW) = 0.84. Those figures come from running this exact tool, so you can reproduce them by entering the same values.
What happens if I enter larger values?
It moves a lot. Using Mechanism = Convection (from a surface), Area A (m²) = 4, Temperature 1 — T₁ (°C, or K for radiation) = 180, Temperature 2 — T₂ (°C, or K for radiation) = 40, Conduction — k (W/m·K) = 1.2, Conduction — thickness d (m) = 0.2, Convection — h (W/m²·K) = 50 and Radiation — emissivity ε (0–1) = 1.8 instead, Heat transfer rate Q (W) goes from 840 to 28,000 — which is why it is worth testing a few scenarios rather than trusting a single figure.
Which “Mechanism” option should I choose?
You can pick between « Conduction (through a wall) », « Convection (from a surface) » and « Radiation (between bodies) ». Each one changes what the calculator works out, so switch and compare — the default is « Conduction (through a wall) ».
What does it give for smaller values?
Scaled down to Mechanism = Conduction (through a wall), Area A (m²) = 1, Temperature 1 — T₁ (°C, or K for radiation) = 45, Temperature 2 — T₂ (°C, or K for radiation) = 10, Conduction — k (W/m·K) = 0.3, Conduction — thickness d (m) = 0.05, Convection — h (W/m²·K) = 12.5 and Radiation — emissivity ε (0–1) = 0.45, Heat transfer rate Q (W) comes out at 210. The relationship is worth checking at both ends before you rely on a single result.
When would I actually use this?
Checking a homework answer, sizing something before building it, and getting an order of magnitude before committing to a design — a torque on a bolt, the force a spring returns, the frequency a circuit resonates at, how long light takes to arrive.
What is the most common mistake?
Feeding in a value in the wrong unit. Physics formulas assume SI throughout, so grams instead of kilograms or centimetres instead of metres shifts the answer by powers of ten without any warning.
How accurate is it, and what are the limits?
Radiation mode expects absolute temperatures in kelvin.
What is the difference between the Heat transfer rate calculator and the Specific heat calculator?
This one returns Heat transfer rate Q (W) and In kilowatts (kW); the Specific heat calculator returns Heat energy (J) and Heat energy (kJ). That is the whole difference — open the one whose figure you need.