Quick answer
Conductive heat flow is Q̇ = k A ΔT ÷ d. An insulation layer with k = 0.04 W/m·K, 20 m² area, 22 K temperature difference and 0.1 m thickness loses 176 W, or 600.5 BTU/h.
Enter conductivity, area, temperature difference and thickness. The calculator returns the heat flow in watts and BTU/h. Use this heat transfer calculator to check your own figures.
Related tools: Specific Heat Calculator: Specific heat capacity or heat required from Q = m c ΔT. Heat Pump COP Calculator: Coefficient of performance from heat output and power input, or the Carnot limit. Thermodynamic Processes Calculator: Work, heat and internal energy for an ideal gas process.
How to use the Heat Transfer Calculator
- Enter thermal conductivity (W/(m·K)) (above 0).
- Enter area (m²) (above 0).
- Enter temperature difference (K).
- Enter thickness (m) (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Thermal conductivity | A number, in W/(m·K) | > 0 |
| Area | A number, in m² | > 0 |
| Temperature difference | A number, in K | — |
| Thickness | A number, in m | > 0 |
Formula and method
Formula
Q̇ = k A ΔT ÷ d; 1 W = 3.412141633 BTU/h
IEEE-754 double precision; shown to the decimals indicated.
One-dimensional steady conduction.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Thermal conductivity = 0.04; Area = 20; Temperature difference = 22; Thickness = 0.1.
| Result | Value |
|---|---|
| Heat flow | 176 W |
| In BTU/h | 600.5369 |
Example 2
Inputs: Thermal conductivity = 205; Area = 0.01; Temperature difference = 50; Thickness = 0.005.
| Result | Value |
|---|---|
| Heat flow | 20,500 W |
| In BTU/h | 69,948.9035 |
Example 3
Inputs: Thermal conductivity = 0.8; Area = 1.5; Temperature difference = 15; Thickness = 0.2.
| Result | Value |
|---|---|
| Heat flow | 90 W |
| In BTU/h | 307.0927 |
The first line is the headline result (heat flow). Below it the heat Transfer Calculator lists in BTU/h, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Worked example
0.04 × 20 × 22 ÷ 0.1 = 176 W. Doubling the thickness halves the loss to 88 W. 176 W × 3.412 = 600.5 BTU/h.
Conduction only
Convection and radiation are not included, and the real loss through a wall also depends on surface films and thermal bridges. Typical k values: mineral wool 0.04, brick 0.7, concrete 1.4, glass 1.0 and copper 400.
How the result changes with thermal conductivity
Holding every other input at the first worked example, this table changes only thermal conductivity. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Thermal conductivity | Heat flow | In BTU/h |
|---|---|---|
| 0.02 | 88 W | 300.2685 |
| 0.04 | 176 W | 600.5369 |
| 0.08 | 352 W | 1,201.0739 |
| 0.16 | 704 W | 2,402.1477 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Thermal conductivity: entering "0" shows "Thermal conductivity must be greater than 0." beside that field and no result.
- Thickness: entering "0" shows "Thickness must be greater than 0." beside that field and no result.
Choosing between the Heat Transfer Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Specific Heat Calculator](/science/specific-heat-calculator/) | solve for, mass and temperature change | Specific heat |
| [Heat Pump COP Calculator](/science/heat-pump-cop-calculator/) | use | COP |
| [Thermodynamic Processes Calculator](/science/thermodynamic-processes/) | process, gas and amount of gas | Work done by the gas |
| [EER Calculator](/science/energy-efficiency-ratio-calculator/) | cooling capacity and power input | EER |
| [Thermal Expansion Calculator](/science/thermal-expansion-calculator/) | coefficient of linear expansion, original length and temperature change | Change in length |
Background: heat and temperature
The basic heat relation is Q = m × c × ΔT: heat in joules equals mass times specific heat capacity times temperature change. A positive Q means heat absorbed and a negative Q heat released, and a change in °C is numerically the same as a change in K.
It covers a change in temperature only. During melting or boiling the temperature stays constant while heat still flows (latent heat), which needs a separate term.
Assumptions and limitations
- Convection and radiation are not included
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for thermal conductivity and thickness to confirm this.
Frequently asked questions
What is thermal conductivity?
How well a material conducts heat.
How do I cut heat loss?
Add insulation or reduce area.
What is the unit?
Thermal conductivity k is in W/(m·K); the example's 0.04 W/(m·K) is typical of mineral wool.
What does the Heat Transfer Calculator calculate?
Conductive heat flow through a flat wall. It returns Heat flow and In BTU/h.
What formula does the Heat Transfer Calculator use?
Q̇ = k A ΔT ÷ d; 1 W = 3.412141633 BTU/h. One-dimensional steady conduction.
What do I need to enter in the heat Transfer Calculator?
You enter Thermal conductivity (W/(m·K)), Area (m²), Temperature difference (K) and Thickness (m).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Convection and radiation are not included.
What is an example of a heat Transfer result?
With thermal conductivity 0.04, area 20, temperature difference 22 and thickness 0.1, the heat flow is 176 W.
Related calculators
- Specific Heat Calculator — Specific heat capacity or heat required from Q = m c ΔT.
- Heat Pump COP Calculator — Coefficient of performance from heat output and power input, or the Carnot limit.
- Thermodynamic Processes Calculator — Work, heat and internal energy for an ideal gas process.
- EER Calculator — Energy efficiency ratio of an air conditioner and its COP equivalent.
- Thermal Expansion Calculator — Change in length from a temperature change.
- Heat Index Calculator — Apparent temperature from air temperature and relative humidity (°F).
Sources
- OpenStax, University Physics Volume 1 (Rice University): mechanics
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.