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Thermal Resistance Calculator

Build a simple series or parallel thermal-resistance network and compute equivalent resistance and heat-transfer rate.

Thermal Resistance inputs

Result section

warningseries

Equivalent thermal resistance

0.3 K/W

Secondary results

Equivalent conductance: 3.33333 W/K
Heat-transfer rate: 33.3333 W
Heat-flow interpretation: Positive heat transfer follows the stated hot-to-cold or heat-added sign convention.

Unit conversion summary

Unit-normalization summary: SI base units; series

Warnings

Thermal properties can vary with temperature, pressure, composition, grade, direction, phase, surface condition, manufacturing process, and data source. Verify all values for the actual operating condition.

Assumptions

Calculations are performed locally in your browser and are not submitted to a third-party calculation API.

Calculation steps

Combine resistance elements0.3 K/W

Thermal resistance network

Req = sum(Ri)

Technical visual

Combine thermal resistances in series or parallel and calculate heat flow from temperature difference.

Engineering interpretation

Positive heat transfer follows the stated hot-to-cold or heat-added sign convention.

What is the thermal resistance calculator?

Use this calculator to combine known K/W thermal resistances before applying a heat-flow temperature difference.

How to use the thermal resistance calculator

Choose series or parallel network mode.
Enter each resistance branch or layer in K/W or equivalent units.
Review equivalent resistance, conductance, and heat-transfer rate.

Input explanations

Series resistances add directly.
Parallel paths add by conductance.
Each resistance is a total K/W resistance, not area-normalized resistance.

Notation

Formula notation
Symbol	Meaning	Unit
Req	Equivalent thermal resistance	K/W
G	Thermal conductance	W/K
delta T	Temperature difference	K

Worked examples

Series R = 0.1 + 0.2 K/W gives Req = 0.3 K/W. Parallel R = 0.1 and 0.2 K/W gives Req = 0.0667 K/W.

Cross-tool workflow

The thermal resistance calculator combines up to five total-resistance elements using series or parallel rules and applies Qdot = delta T / Req.

Use equivalent resistance in conduction

Common mistakes

Combining m2 K/W values with K/W values.
Using parallel formulas for a layered one-dimensional wall.
Forgetting that contact and film resistances may dominate.

Limitations

Thermal properties are treated as constant user-entered values.
The tool does not select material, fluid, steam, refrigerant, phase-change, or fouling data automatically.
Results are preliminary engineering estimates and do not certify code compliance or safety.
Multidimensional effects, transient storage, contact details, and property variation must be evaluated separately when important.
Network topology is limited to all-series or all-parallel groups.

References

Fundamentals of Heat and Mass Transfer: Incropera, DeWitt, Bergman, and Lavine, Fundamentals of Heat and Mass Transfer.
Heat and Mass Transfer: Cengel and Ghajar, Heat and Mass Transfer: Fundamentals and Applications.
Heat Transfer: Holman, Heat Transfer.
Compact Heat Exchangers: Kays and London, Compact Heat Exchangers.
SI units: BIPM, The International System of Units (SI Brochure).
NIST unit guidance: NIST Special Publication 811, Guide for the Use of the International System of Units.

What assumptions does the thermal resistance calculator use?

It uses the stated steady or lumped formula with user-entered properties and does not infer hidden losses, standards factors, or temperature-dependent property data.

Are Celsius and Fahrenheit temperature differences handled as offsets?

No. Absolute temperature and temperature difference are separate quantities. Temperature differences use delta units without absolute-temperature offsets.

Can I use the result for final design approval?

No. Use the result for education, estimation, and preliminary review only. Critical work must be checked with standards, validated software, measured properties, and qualified engineering judgment.

Does the calculation run on a remote thermal-property API?

No. Calculations are performed locally in your browser and are not submitted to a third-party calculation API.

Engineering disclaimer

This tool is intended for educational, estimation, and preliminary engineering use. Always verify critical heat-transfer calculations with applicable standards, validated software, measured properties, and qualified professional judgment before using results in real design, manufacturing, construction, safety, or compliance decisions.

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Last reviewed: 2026-06-30

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Thermal Resistance inputs

Result section

warningseries

Equivalent thermal resistance

0.3 K/W

Secondary results

Equivalent conductance: 3.33333 W/K
Heat-transfer rate: 33.3333 W
Heat-flow interpretation: Positive heat transfer follows the stated hot-to-cold or heat-added sign convention.

Unit conversion summary

Unit-normalization summary: SI base units; series

Warnings

Thermal properties can vary with temperature, pressure, composition, grade, direction, phase, surface condition, manufacturing process, and data source. Verify all values for the actual operating condition.

Assumptions

Calculations are performed locally in your browser and are not submitted to a third-party calculation API.

Calculation steps

Combine resistance elements0.3 K/W

Thermal resistance network

Req = sum(Ri)

Symbol

Meaning

Unit

Req

Equivalent thermal resistance

K/W

Thermal conductance

W/K

delta T

Temperature difference

Limitations

Thermal properties are treated as constant user-entered values.

The tool does not select material, fluid, steam, refrigerant, phase-change, or fouling data automatically.

Results are preliminary engineering estimates and do not certify code compliance or safety.

Multidimensional effects, transient storage, contact details, and property variation must be evaluated separately when important.

Network topology is limited to all-series or all-parallel groups.

References

Fundamentals of Heat and Mass Transfer: Incropera, DeWitt, Bergman, and Lavine, Fundamentals of Heat and Mass Transfer.

Heat and Mass Transfer: Cengel and Ghajar, Heat and Mass Transfer: Fundamentals and Applications.

Heat Transfer: Holman, Heat Transfer.

Compact Heat Exchangers: Kays and London, Compact Heat Exchangers.

SI units: BIPM, The International System of Units (SI Brochure).

NIST unit guidance: NIST Special Publication 811, Guide for the Use of the International System of Units.

Engineering disclaimer

Thermal Resistance inputs

Calculation mode

Thermal resistance network

Resistance elements

Result section

Secondary results

Unit conversion summary

Warnings

Assumptions

Calculation steps

Thermal resistance network

Technical visual

Engineering interpretation

What is the thermal resistance calculator?

How to use the thermal resistance calculator

Input explanations

Notation

Worked examples

Cross-tool workflow

Common mistakes

Limitations

References

Related tools

Print summary

Engineering disclaimer

Need Professional Support?

Thermal Resistance inputs

Calculation mode

Thermal resistance network

Resistance elements

Result section

Secondary results

Unit conversion summary

Warnings

Assumptions

Calculation steps

Thermal resistance network

Technical visual

Engineering interpretation

What is the thermal resistance calculator?

How to use the thermal resistance calculator

Input explanations

Notation

Worked examples

Cross-tool workflow

Common mistakes

Limitations

References

Related tools

Print summary

Engineering disclaimer

Need Professional Support?