Fin and Heat Sink Calculator: Fin Efficiency, Effectiveness, Heat Dissipation and Thermal Resistance

Size a heat sink or an extended surface, with the working.

Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.

How this calculator works

Choose the fin material and enter the heat transfer coefficient, the fin thickness, height and length.

Enter the base and air temperatures, the number of fins and the width of the base plate.

The calculator gives the heat from one fin, its efficiency and effectiveness, the tip temperature, the heat from the whole sink and its thermal resistance.

Formulas used

  • m = \sqrt{\frac{hP}{kA}}
  • q_f = \sqrt{hPkA}\,\theta_b\tanh(mL_c)
  • \eta_f = \frac{\tanh(mL_c)}{mL_c}
  • R_\theta = \frac{\theta_b}{q}

Worked example

With the default numbers in the calculator above:

  1. Fin parameter m (a bigger m means the heat dies away faster along the fin): 12.357 per metre
  2. Corrected length (allows for heat lost from the tip): 31 mm
  3. Heat lost from one fin: 8.2937 W
  4. Fin efficiency (the heat lost compared with a fin that is all at the base temperature): 95.38 %
  5. Fin effectiveness (the heat lost compared with the bare base area where the fin is attached): 30.16
  6. Temperature at the fin tip: 76.197 C
  7. Heat from the whole heat sink: fins plus the bare base between them: 88.437 W
  8. Thermal resistance from the base to the air: 0.6219 K/W
  9. Gap between the fins: 4.444 mm

Change the numbers in the calculator to see the full working, every step, for your own case.

Common questions

What is fin efficiency?

The heat the fin really loses divided by the heat it would lose if all of it were at the base temperature.

Why do fins help?

They add surface area for heat to leave by convection. They help most where the heat transfer coefficient is low, such as with still air.

What is the thermal resistance of a heat sink?

The temperature rise of the base above the air for each watt of heat. A lower number is a better heat sink.

Related calculators

Got a question about this? Ask an engineering question and get a plain-language answer with references.

Further reading: Any heat transfer text (extended surfaces, fin equations).

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