Thermal Resistance Calculator for Gap Pads & Interface Materials
Compute the conduction resistance and temperature rise a thermal interface pad adds between a component and its heat sink: R = t/(k×A), ΔT = Q×R — the first numbers you need when sizing a gap filler.
Built for: sizing gap pads so junctions stay inside their rated temperature, and comparing TIM families before sampling.
Thermal Resistance Calculator
How it works — formula, worked example & reference
Formula: R = t / (k × A) (one-dimensional Fourier conduction); temperature rise ΔT = Q × R. Pad conductivity is measured per ASTM D5470.
Worked example: t = 1.0 mm, k = 3.0 W/m·K, A = 25 mm², Q = 5 W: R = 0.001 / (3.0 × 25×10⁻⁶) = 13.3 °C/W; ΔT = 5 × 13.3 = 66.7 °C.
| Gap-pad family | Thermal conductivity (W/m·K) |
|---|---|
| Sil-Pad® | 0.9–3.5 |
| Gap Pad® | 1.0–6.5 |
| HiTherm® TC | 2.0–4.0 |
| Tflex™ / Tputty | 1.0–5.5 |
Ranges per H-O material catalog; use the exact value from your material data sheet.
These results are engineering estimates for preliminary material selection; final validation is the responsibility of your engineering team.
Common questions
How do you calculate thermal resistance?
For conduction through a flat layer, R = t / (k × A): thickness divided by thermal conductivity times area. The result is in °C/W (equivalently K/W) — multiply by the heat flow to get temperature rise.
What is a good thermal resistance for a gap pad?
Lower is better; what is ‘good’ depends on the power. The pad’s share of the budget follows from ΔT = Q × R — at 5 W, 13 °C/W adds 67 °C, which usually forces a thinner or higher-k pad.
Thermal resistance vs thermal impedance?
Resistance (t/kA) is the bulk-material term. Impedance, measured per ASTM D5470, adds the two contact resistances at the surfaces — it is what you actually see in an assembly and is always higher than the bulk number.
How do I lower the temperature rise?
Thinner bond line, higher-conductivity material, or more area. The calculator makes the trade-offs explicit — halving thickness halves R; doubling area halves it too.